PerlMagick (a perl interface to the ImageMagick tool) is just what you need. It is the swiss-army knife of perl image manipulation libraries. PerlMagick comes with the standard ImageMagic distribution. ImageMagick can handle many image formats including: BMP, GIF, PNG, JPG (many more, see the full list). The actual PerlMagick code is pretty simple to use in your application:

  use Image::Magick;

  my $im=new Image::Magick;    
  $im->Read($fname);
  $im->Annotate(text=>'some text');  
  $im->Set(format=>'Joint Photographic Experts Group JFIF format');
  $im->Write();
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PerlMagick can also do many "photoshop-type" editing effects (Crop, Scale, Blur, Despeckle, etc). It is big but I have yet to fins a more powerful image manipulation tool under Perl.