Avatars can be a BMP, GIF or JPG image.. or other. They have a file name, and you can find their origin by right-clicking on the image and choosing 'properties'.
Likely many of the Avatars and icons from years back are no longer available, due to "downsizing" or not being popular. Any specific Avatar you want can be used, as long as it is in good taste (not offensive), and meets the space requirements for such. Use any trusted hosting site for your image, or upload it to the Forum for access. Use the command string
for those residing on our Forum. For those on hosting sites, use their IP address with the appropriate file name.
F@H.. to solve mankind's maladies.. in our lifetimes!