#!/usr/bin/perl -wT
use strict;
use CGI;

my $cgi = CGI->new;

my ($id) = $cgi->param('id') =~ /^(\w+)$/;
my $filename = "$id.png";

my $content = eval {
    open my $fh, '<', "images/$filename" or die "Open failure: $!";
    binmode $fh;
    <$fh>;
}

print $cgi->header(-type  =>  'image/png',
                   -expires   =>  '+1h',
                   -content_disposition=>"inline; filename=$filename"
                   );
if ($content) {
    print $content
} else {
    open my $fh, 'images/none.png' or die;
    binmode $fh;
    print <$fh>;
}