#!/usr/bin/perl -w
use strict;
use CGI qw(:standard);
use CGI::Carp;

my $path = "/path/to/images";
my $imagereq = param('iwant');

$imagereq ||= 0; # defaults to image 0

my $image_path = "$path/$imagereq.jpg";

# check there are digits only in the request and that the file exists
$image_path = "$path/404.jpg" unless $imagereq =~ /^\d+$/ and -e $image_path;

open(IMAGE, "<", $image_path) or die "ACK! $!";
print "Content-type: image/jpeg\n\n";
binmode STDOUT;

$/ = \8192; # read data in 8kbyte chunks rather than from LF to LF
            # see perldoc perlvar

print while <IMAGE>;