1. Take full image link
Code:
http://oi54.tinypic.com/29ehwkl.jpg
2. Add _th after the file name (before the extension)
Code:
http://oi54.tinypic.com/29ehwkl_th.jpg
3. Add [img] tags.
Code:
[img]http://oi54.tinypic.com/29ehwkl_th.jpg[/img]
4. Add [url=full_link_from_#1][/url] tags.
Code:
[url=http://oi54.tinypic.com/29ehwkl.jpg][img]http://oi54.tinypic.com/29ehwkl_th.jpg[/img][/url]
5. Done


Thanks to whoever I stole that screenshot from.