You don't need a handler to do what you want. Use the path_info method from CGI.

Write a CGI script img (or whatever) whose sole purpose is to feed user images. e.g:

#!/usr/bin/perl -w

use strict;
use CGI;

my $q = new CGI;

my ($user) = split m!/!, $q->path_info();

# database connection stuff here ...
# fetch $pic from database for $user

pint $q->header("image/jpeg"), $pic;
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