Isn't it possible to get a thumb that is clickable?

You had the url in there twice. Put the image in where you had the repeated url, like this:

[url=http://www.fractalforums.com/index.php?action=gallery;sa=view;id=5723][img]http://nocache-nocookies.digitalgott.com/gallery/5/thumb_1002_18_02_11_9_13_41.jpeg[/img][/url]
[url=http://www.fractalforums.com/index.php?action=gallery;sa=view;id=5722] [img]http://nocache-nocookies.digitalgott.com/gallery/5/thumb_1002_18_02_11_9_10_39.jpeg[/img][/url]