Okay I copied Dr Unne's code, set up a webserver here on my computer, and put the cgi file in there. I then put two images in the directory.

It doesn't work. I get a red 'x' when I run the html file that has the image tag.

Code:
#!/usr/bin/perl -T

use strict;
use warnings;

use CGI;

my $filename = int(rand(2));

($filename == 1) ? ($filename = 'F_H.jpg') : ($filename = 'takebacktheweb_large.jpg');

if(open FILE, "<", $filename) {
	print CGI::header('image/png');
	binmode FILE;
	print while(<FILE>);
	close FILE;
} else {
	print CGI::header();
	print "Error: $!";
}
Code:
[html]
[body]
[img src="http://192.168.2.103/pics.cgi" /]
[/body]
[/html]