set_form_variables # preference (right now, one of 4base_jpeg, base_jpeg, base_fpx, base4_fpx) ns_return $conn 200 "text/html Pragma: no-cache Set-Cookie: thumbnail_preference=$preference; path=/; expires=Fri, 01-Jan-2010 01:00:00 GMT" " Thumbnail Preference Set

Thumbnail Preference Set

Unless your browser is ancient and does not accept cookies, you should be all set up now. Try it out by clicking on the image below...

(from my guidebook to Italy)