The London Perl and Raku Workshop takes place on 26th Oct 2024. If your company depends on Perl, please consider sponsoring and/or attending.


GD::SecurityImage - Security image (captcha) generator.


   use GD::SecurityImage;

   # Create a normal image
   my $image = GD::SecurityImage->new(
                  width   => 80,
                  height  => 30,
                  lines   => 10,
                  gd_font => 'giant',
      $image->random( $your_random_str );
      $image->create( normal => 'rect' );
   my($image_data, $mime_type, $random_number) = $image->out;


   # use external ttf font
   my $image = GD::SecurityImage->new(
                  width    => 100,
                  height   => 40,
                  lines    => 10,
                  font     => "/absolute/path/to/your.ttf",
                  scramble => 1,
      $image->random( $your_random_str );
      $image->create( ttf => 'default' );
   my($image_data, $mime_type, $random_number) = $image->out;

or you can just say (most of the public methods can be chained)

   my($image, $type, $rnd) = GD::SecurityImage->new->random->create->particle->out;

to create a security image with the default settings. But that may not be useful. If you require the module, you must import it:

   require GD::SecurityImage;

The module also supports Image::Magick, but the default interface uses the GD module. To enable Image::Magick support, you must call the module with the use_magick option:

   use GD::SecurityImage use_magick => 1;

If you require the module, you must import it:

   require GD::SecurityImage;
   GD::SecurityImage->import(use_magick => 1);

The module does not export anything actually. But import loads the necessary sub modules. If you don' t import, the required modules will not be loaded and probably, you'll die().


This document describes version 1.73 of GD::SecurityImage released on 21 January 2015.

The (so called) "Security Images" are so popular. Most internet software use these in their registration screens to block robot programs (which may register tons of fake member accounts). Security images are basicaly, graphical CAPTCHAs (Completely Automated Public Turing Test to Tell Computers and Humans Apart). This module gives you a basic interface to create such an image. The final output is the actual graphic data, the mime type of the graphic and the created random string. The module also has some "styles" that are used to create the background (or foreground) of the image.

If you are an Authen::Captcha user, see GD::SecurityImage::AC for migration from Authen::Captcha to GD::SecurityImage.

This module is just an image generator. Not a captcha handler. The validation of the generated graphic is left to your programming taste. But there are some captcha handlers for several Perl FrameWorks. If you are an user of one of these frameworks, see "GD::SecurityImage Implementations" in "SEE ALSO" section for information.


This module can use both RGB and HEX values as the color parameters. HEX values are recommended, since they are widely used and recognised.

   $color  = '#80C0F0';     # HEX
   $color2 = [15, 100, 75]; # RGB
   $i->create($meth, $style, $color, $color2)

   $i->create(ttf => 'box', '#80C0F0', '#0F644B')

RGB values must be passed as an array reference including the three Red, Green and Blue values.

Color conversion is transparent to the user. You can use hex values under both GD and Image::Magick. They' ll be automagically converted to RGB if you are under GD.



The constructor. new() method takes several arguments. These arguments are listed below.


The width of the image (in pixels).


The height of the image (in pixels).


Numerical value. The point size of the ttf character. Only necessarry if you want to use a ttf font in the image.


The number of lines that you' ll see in the background of the image. The alignment of lines can be vertical, horizontal or angled or all of them. If you increase this parameter' s value, the image will be more cryptic.


The absolute path to your TrueType (.ttf) font file. Be aware that relative font paths are not recognized due to problems in the libgd library.

If you are sure that you've set this parameter to a correct value and you get warnings or you get an empty image, be sure that your path does not include spaces in it. It looks like libgd also have problems with this kind of paths (eg: '/Documents and Settings/user' under Windows).

Set this parameter if you want to use ttf in your image.


If you want to use the default interface, set this parameter. The recognized values are Small, Large, MediumBold, Tiny, Giant. The names are case-insensitive; you can pass lower-cased parameters.


The background color of the image.


If has a true value, the random security code will be displayed in the background and the lines will pass over it. (send_ctobg = send code to background)


If has a true value, a frame will be added around the image. This option is enabled by default.


If set, the characters will be scrambled. If you enable this option, be sure to use a wider image, since the characters will be separated with three spaces.


Sets the angle for scrambled/normal characters. Beware that, if you pass an angle parameter, the characters in your random string will have a fixed angle. If you do not set an angle parameter, the angle(s) will be random.

When the scramble option is not enabled, this parameter still controls the angle of the text. But, since the text will be centered inside the image, using this parameter without scramble option will require a taller image. Clipping will occur with smaller height values.

Unlike the GD interface, angle is in degrees and can take values between 0 and 360.


Sets the line drawing width. Can take numerical values. Default values are 1 for GD and 0.6 for Image:Magick.


The minimum length of the random string. Default value is 6.


Default character set used to create the random string is 0..9. But, if you want to use letters also, you can set this parameter. This parameter takes an array reference as the value.

Not necessary and will not be used if you pass your own random string.


Creates the random security string or sets the random string to the value you have passed. If you pass your own random string, be aware that it must be at least six (defined in rndmax) characters long.


Returns the random string. Must be called after random().


This method creates the actual image. It takes four arguments, but none are mandatory.

   $image->create($method, $style, $text_color, $line_color);

$method can be normal or ttf.

$style can be one of the following (some of the styles may not work if you are using a really old version of GD):


The default style. Draws horizontal, vertical and angular lines.


Draws horizontal and vertical lines


Draws two filled rectangles.

The lines option passed to new, controls the size of the inner rectangle for this style. If you increase the lines, you'll get a smaller internal rectangle. Using smaller values like 5 can be better.


Draws circles.


Draws ellipses.


This is the combination of ellipse and circle styles. Draws both ellipses and circles.


Draws nothing. See "OTHER USES".

Note: if you have a (too) old version of GD, you may not be able to use some of the styles.

You can use this code to get all available style names:

   my @styles = grep {s/^style_//} keys %GD::SecurityImage::Styles::;

The last two arguments ($text_color and $line_color) are the colors used in the image (text and line color -- respectively):

   $image->create($method, $style, [0,0,0], [200,200,200]);
   $image->create($method, $style, '#000000', '#c8c8c8');


Must be called after create.

Adds random dots to the image. They'll cover all over the surface. Accepts two parameters; the density (number) of the particles and the maximum number of dots around the main dot.

   $image->particle($density, $maxdots);

Default value of $density is dependent on your image' s width or height value. The greater value of width and height is taken and multiplied by twenty. So; if your width is 200 and height is 70, $density is 200 * 20 = 4000 (unless you pass your own value). The default value of $density can be too much for smaller images.

$maxdots defines the maximum number of dots near the default dot. Default value is 1. If you set it to 4, The selected pixel and 3 other pixels near it will be used and colored.

The color of the particles are the same as the color of your text (defined in create).


This method must be called after create. If you call it early, you'll die. info_text adds an extra text to the generated image. You can also put a strip under the text. The purpose of this method is to display additional information on the image. Copyright information can be an example for that.

      x      => 'right',
      y      => 'up',
      gd     => 1,
      strip  => 1,
      color  => '#000000',
      scolor => '#FFFFFF',
      text   => 'Generated by GD::SecurityImage',



Controls the horizontal location of the information text. Can be either left or right.


Controls the vertical location of the information text. Can be either up or down.


If has a true value, a strip will be added to the background of the information text.


This option can only be used under GD. Has no effect under Image::Magick. If has a true value, the standard GD font Tiny will be used for the information text.

If this option is not present or has a false value, the TTF font parameter passed to new will be used instead.


The ptsize value of the information text to be used with the TTF font. TTF font parameter can not be set with info_text(). The value passed to new() will be used instead.


The color of the information text.


The color of the strip.


This parameter controls the displayed text. If you want to display long texts, be sure to adjust the image, or clipping will occur.


This method finally returns the created image, the mime type of the image and the random number(s) generated. Older versions of GD only support gif type, while new versions support jpeg and png (update: beginning with v2.15, GD resumed gif support).

The returned mime type is png or gif or jpeg for GD and gif for Image::Magick (if you do not force some other format).

out method accepts arguments:

   @data = $image->out(%args);

You can set the output format with the force parameter:

   @data = $image->out(force => 'png');

If png is supported by the interface (via GD or Image::Magick); you'll get a png image, if the interface does not support this format, out() method will use it's default configuration.


And with the compress parameter, you can define the compression for png and quality for jpeg:

   @data = $image->out(force => 'png' , compress => 1);
   @data = $image->out(force => 'jpeg', compress => 100);

When you use compress with png format, the value of compress is ignored and it is only checked if it has a true value. With png the compression will always be 9 (maximum compression). eg:

   @data = $image->out(force => 'png' , compress => 1);
   @data = $image->out(force => 'png' , compress => 3);
   @data = $image->out(force => 'png' , compress => 5);
   @data = $image->out(force => 'png' , compress => 1500);

All will default to 9. But this will disable compression:

   @data = $image->out(force => 'png' , compress => 0);

But the behaviour changes if the format is jpeg; the value of compress will be used for jpeg quality; which is in the range 1..100.

Compression and quality operations are disabled by default.


Depending on your usage of the module; returns the raw GD::Image object:

   my $gd = $image->raw;
   print $gd->png;

or the raw Image::Magick object:

   my $magick = $image->raw;

Can be useful, if you want to modify the graphic yourself. If you want to get an image type see the force option in out.


See "path bug" in "GD bug" for usage and other information on this method.










Returns a list of available GD::SecurityImage back-ends.

   my @be = GD::SecurityImage->backends;


   my @be = $image->backends;

If called in a void context, prints a verbose list of available GD::SecurityImage back-ends:

   Available back-ends in GD::SecurityImage v1.55 are:
   Search directories:

you can see the output with this command:

   perl -MGD::SecurityImage -e 'GD::SecurityImage->backends'

or under windows:

   perl -MGD::SecurityImage -e "GD::SecurityImage->backends"


See the tests in the distribution. Also see the demo program "eg/" for an Apache::Session implementation of GD::SecurityImage.

Download the distribution from a CPAN mirror near you, if you don't have the files.


All TTF samples generated with the bundled font StayPuft.ttf, unless stated otherwise. Most of the samples here can be generated with running the test suite that comes with the GD::SecurityImage distribution. However, images that are generated with random angles will indeed be a little different after you run the test suite on your system.

All random codes have a length of six (6) characters, unless stated otherwise. So, (for example) there is no clipping in ELLIPS.

Images generated with GD

Standard interface. Font: gdGiantFont Style: rect
Style: rect. Scrambled with random angles. Style: circle. Scrambled with a fixed angle.
Style: default. Scrambled with a fixed angle.
Info text at the top right.
Style: circle. Scrambled with random angles.
Font is: Transformers.ttf


Images generated with Image::Magick

Style: circle. Style: box. Scrambled with random angles.
Style: circle. Scrambled with a fixed angle. Style: ellipse. Scrambled with a fixed angle.
Info text at the top right.
Style: ec. Scrambled with random angles.
Info text at the top right.
Style: ec. Scrambled with random angles1.

1: This image is generated with this code:

use GD::SecurityImage backend => 'Magick';
my($data, $mime, $rnd) = GD::SecurityImage
   width      => 420,
   height     => 100,
   ptsize     => 40,
   lines      => 20,
   thickness  => 4,
   rndmax     => 5,
   scramble   => 1,
   send_ctobg => 1,
   bgcolor    => '#009999',
   font       => 'StayPuft.ttf',
->create( qw/ ttf ec #0066CC #0066CC / )
->particle(300, 500)

Images hosted by ImageShack.


GD::SecurityImage drawing capabilities can also be used for counter image generation or displaying arbitrary messages:

   use CGI qw(header);
   use GD::SecurityImage 1.64; # we need the "blank" style
   my $font  = "StayPuft.ttf";
   my $rnd   = "10.257"; # counter data
   my $image = GD::SecurityImage->new(
      width  =>   140,
      height =>    75,
      ptsize =>    30,
      rndmax =>     1, # keeping this low helps to display short strings
      frame  =>     0, # disable borders
      font   => $font,
   $image->random( $rnd );
   # use the blank style, so that nothing will be drawn
   # to distort the image.
   $image->create( ttf => 'blank', '#CC8A00' );
      text   => 'You are visitor number',
      ptsize => 10,
      strip  =>  0,
      color  => '#0094CC',
      text   => '( c ) 2 0 0 7   m y s i t e',
      ptsize => 10,
      strip  =>  0,
      color  => '#d7d7d7',
      y      => 'down',
   my($data, $mime, $random) = $image->out;
   binmode STDOUT;
   print header -type => "image/$mime";
   print $data;

The generated graphic will be:

Image Hosted by

Image hosted by ImageShack.


die is called in some methods if something fails. You may need to eval your code to catch exceptions.


If you look at the demo program (not just look at it, try to run it) you'll see that the random code changes after every request (successful or not). If you do not change the random code after a failed request and display the random code inside HTML (like "Wrong! It must be <random>"), then you are doing a logical mistake, since the user (or robot) can now copy & paste the random code into your validator without looking at the security image and will pass the test. Just don't do that. Random code must change after every validation.

If you want to be a little more strict, you can also add a timeout key to the session (this feature currently does not exits in the demo) and expire the related random code after the timeout. Since robots can call the image generator directly (without requiring the HTML form), they can examine the image for a while without changing it. A timeout implemetation may prevent this.


See the "SUPPORT" section if you have a bug or request to report.

Image::Magick bug

There is a bug in PerlMagick' s QueryFontMetrics() method. ImageMagick versions smaller than 6.0.4 is affected. Below text is from the ImageMagick 6.0.4 Changelog:

"2004-05-06 PerlMagick's QueryFontMetrics() incorrectly reports `unrecognized attribute'` for the `font' attribute."

Please upgrade to ImageMagick 6.0.4 or any newer version, if your ImageMagick version is smaller than 6.0.4 and you want to use Image::Magick as the backend for GD::SecurityImage.

GD bug

path bug

libgd and don't like relative paths and paths that have spaces in them. If you pass a font path that is not an exact path or a path that have a space in it, you may get an empty image.

To check if the module failed to find the ttf font (when using GD), a new method added: gdbox_empty(). It must be called after create():

   die "Error loading ttf font for GD: $@" if $image->gdbox_empty;

gdbox_empty() always returns false, if you are using Image::Magick.


Wrong GD installation

I got some error reports saying that GD::SecurityImage dies with this error:

   Can't locate object method "new" via package "GD::Image" 
   (perhaps you forgot to load "GD::Image"?) at ...

This is due to a wrong installation of the GD module. GD includes XS code and it needs to be compiled. You can't just copy/paste the and expect it to work. It will not. If you are under Windows and don't have a C compiler, you have to add new repositories to install GD, since ActiveState' s own repositories don't include GD. Randy Kobes and J-L Morel have ppm repositories for both 5.6.x and 5.8.x and they both have GD: also has a GD::SecurityImage ppd, so you can just install GD::SecurityImage from that repository.

libgd errors

There are some issues related to wrong/incomplete compiling of libgd and old/new version conflicts.

libgd without TTF support

If your libgd is compiled without TTF support, you'll get an empty image. The lines will be drawn, but there will be no text. You can check it with "gdbox_empty" method.

GIF - Old libgd or libgd without GIF support enabled

If your GD has a gif method, but you get empty images with gif() method, you have to update your libgd or compile it with GIF enabled.

You can test if gif is working from the command line:

   perl -MGD -e '$_=GD::Image->new;$_->colorAllocate(0,0,0);print$_->gif'

or under windows:

   perl -MGD -e "$_=GD::Image->new;$_->colorAllocate(0,0,0);print$_->gif"


  • If it dies, your GD is very old.

  • If it prints nothing, your libgd was compiled without GIF enabled (upgrade or re-compile).

  • If it prints out a junk that starts with 'GIF87a', everything is OK.


  • Using the default library GD is a better choice. Since it is faster and does not use that much memory, while Image::Magick is slower and uses more memory.

  • The internal random code generator is used only for demonstration purposes for this module. It may not be effective. You must supply your own random code and use this module to display it.

  • [GD] png compression

    Support for compression level argument to png() added in v2.07. If your GD version is smaller than this, compress option to out() will be silently ignored.

  • [GD] setThickness

    setThickness implemented in GD v2.07. If your GD version is smaller than that and you set thickness option, nothing will happen.

  • [GD] ellipse

    ellipse() method added in GD 2.07.

    If your GD version is smaller than 2.07 and you use ellipse, the default style will be returned.

    If your GD is smaller than 2.07 and you use ec, only the circles will be drawn.


Other CAPTCHA Implementations & Perl Modules

GD::SecurityImage Implementations

Software Using GD::SecurityImage

If your software uses GD::SecurityImage for captcha generation and want to appear in this document, contact the author.



All bug reports and wishlist items must be reported via the CPAN RT system. It is accessible at


CPAN::Forum is a place for discussing CPAN modules. It also has a GD::SecurityImage section at


If you like or hate or have some suggestions about GD::SecurityImage, you can comment/rate the distribution via the CPAN Ratings system:


Burak Gursoy <>.


Copyright 2004 - 2015 Burak Gursoy. All rights reserved.


This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.12.4 or, at your option, any later version of Perl 5 you may have available.