Use ImageMagick. It is really powerful. ImageMagick can be controlled with perl, using the module Image::Magick. In FC4 this can be installed with "yum install ImageMagick-perl"

You weren't specific about how you'd like the images combined. I'll let you play with the different imagemagick options. Here's some code to get you started.

#!/usr/bin/perl
use warnings;
use strict;
use Image::Magick;

my $image1=new Image::Magick;
$image1->Read("dir1/1.gif");
my $image2=new Image::Magick;
$image2->Read("dir1/2.gif");
$image1->Composite(image=>$image2,compose=>'plus');
$image1->Write("dir1.psd");
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