You can do that from your Photobucket account.

Click the little selectbox next to the name of the file(s) you want to post as a clickable thumbnail.
Then go to the bottom of the page and click the 'Generate HTML and Image Code' button
A screen will show that gives you several different codes.
Click inside the box that says "IMG clickable thumbnails for message boards - recommended" and it will say 'copied'.
You can then paste that code into a reply and a clickable thumbnail will show up.


This is recommendable when you have really large pictures, or pictures that may not be of interest to everyone (like your own vacation pictures or something) so people wont have to scroll past (and wait for the loading off) lots of pictures they may not want to see that badly.. (not that I wouldn't want to see your vacation pics Emi.. it's just an example.. )