Look at URI::data
I'm not that familiar with Mason but with CGI you can do something like this:

#assuming $image contains the gif and $q is a CGI object

use URI;
my $u = URI->new("data:");
$u->media_type("image/gif");
$u->data($image);
print $q->img(-src => "$u");
[download]

Note: this code is untested and not all browsers can handle this.

--

flounder