My guess (since you didn't say) is that you're on ActiveState Perl and you forgot to say binmode on your GIF handle.

But you can avoid even that by using a very efficient file-copy method:

use File::Copy;
print "Content-type: image/gif\n\n";
copy "/path/to/gif", \*STDOUT;
[download]

-- Randal L. Schwartz, Perl hacker