Step One.
Upload your picture on to photobucket and highlight and copy the "direct link".

Step Two.
Then when you come to Gaia and click "reply," use the BBcode button for URL. Paste the "direct link" into the pop up you get from the url button.

Step Three Part One
After you click "okay," the box will change and say "website text." Clear that out and put the image tags in.

Step Three Part Two.
Paste the "direct link" again inside the image tags. Once the link is there inside the image tags, go to the end of the URL and after the last back slash [ / ] before the file name (whatever ends in .jpg or .png or whatever picture file it is) ad "th_" which is the coding for "thumbnail." Hit enter again.

The coding should look like this, red being the direct link, yellow being the image tags, and green being the "thumbnail" converter.

It's that easy! ;D