Here is a .png file for people to right-click and download, which is a color-matched to the panel for your forum avatar (
https://postimg.org/image/5jecceupz/):
The next file is a .tif file to also right-click and download, that has Layers, in case you use Photoshop or something else:
https://drive.google.com/open?id=0B4WGk ... UxjVEloZmM
Anyway, the purpose is that if you do not have a 150x150 pixel image to place for your avatar, you can open either of these files in a graphics editor, copy and paste your current avatar on top, center it, then re-save as a new file. Then upload. This way, your smaller image will look all centered and nice.
If you're even more savvy with graphics, you can utilize the background to make transparent PNGs, like my own avatar. Or, if you find a transparent PNG/GIF on the internet and wish to use it, you know have a color matched background to work with.