I use the following html to display an image via a perl script:

<img src="randimage.cgi" border="2" alt="[mini-beast]">
[download]

Where randimage.cgi is:

#!/usr/bin/perl -wT
use strict;
my @files = glob("./jpegs/*.jpg");
print "Location: $files[int(rand @files)]\n\n";
[download]

If that's any help...

...and, no, I don't know what the 'Location: ' and two newlines are for - I can only assume that they are normally output by a web-server as part of the protocol...

... okay, looked 'Location: ' up - it's a redirection command, which makes sense.