If you tried uploading the image you are hotlinking to right now, it was probably rejected because it is too big--656 x 901. In fact, you'd probably have a moderator sticking width or height directives to the image tags if you posted it to the forum!
If you resample down to 65 pixels maximum in each dimension, it should upload. I uploaded mine successfully.
Edit: Since the image is hotlinked from your site, (1) forum users need to load the full image when they read a thread you have posted in, even though it will render on their browsers with less than a hundredth of the pixel count, and (2) the bandwidth consumed to load the redundant data is charged against your hosting account.