I'd also suggest that

for (@image_extensions) {
  if ($url =~ /\.${_}$/) {
[download]

for my $ext (@image_extensions) {
  if ($url =~ /\.$ext$) {
[download]

gav^

This isn't necessary, but what if .jpg becomes a domain suffix?

use URI;

my $addr     = URI->new($url);
my $path     = $addr->path;

for my $ext (@image_extensions) {
    if ($path =~ /\.$ext$/) {
    ....
[download]

Probably not worth it to add this in, but I thought I'd point it out anyways :).

OK, here's a complete (non-tested :) version...

#!/usr/local/bin/perl -w
use strict;
use CGI;
my $q = new CGI;

my @image_extensions = qw(gif png jpg jpeg);

my $referer = $ENV{'HTTP_REFERER'};
my $user = $ENV{'REMOTE_ADDR'};
my $usercomp = $ENV{'REMOTE_HOST'};
my $url = $ENV{'REDIRECT_URL'};
my $gmt = gmtime(time);

if ($referer) {
  open(FILE2,">>public/404.txt");
  print FILE2 "$url|$referer|$user|$usercomp|$gmt\n";
  close(FILE2);
}

for (@image_extensions) {
  if ($url =~ /\.${_}$/) {
    print $q->redirect(-uri=>'http://image.url/here.gif');
    exit(0);
  }
}

print $q->header,
      $q->start_html,
      $q->h1('Whoops!'),
      $q->h3($url),
      $q->p('That page does not exist. Please press your back button a
+nd try again.'),
      $q->end_html;
exit(0);
[download]

cLive ;-)

--
seek(JOB,$$LA,0);

cLive, I love you and I want to have your babies. *MWAH* :)

If you made that an internal redirect rather than an external redirect, the browser wouldn't have to pull a second hit from the server... the server would merely substitute the image data.

...
for (@image_extensions) {
  if ($url =~ /\.$_\z/) {
    print $q->redirect("/image/url/here.gif");
    exit 0;
  }
}
...
[download]

Now, about them babies... {grin}

-- Randal L. Schwartz, Perl hacker