1. Make an account with Photobucket (its very easy and takes about a minute)
2. Upload your picture
3. Make a tick in the box of the picture(s) you wish to post

4. Scroll to the bottom and click the option to Generate HTML and IMG Code

5. After a few seconds (depending on how many pictures you have ticked)
you will get a list of options, select the IMG clickable thumbnails option

6. Copy the entire section of code and simply paste it into your post and submit ..
The forum is restricted to a maximum size of 600 x 600, be it full pictures or thumbnail images ... this restriction obviously doesn't apply to the image that opens once you thumbnail is clicking in the post, that image can be as big or small as you wish ..