It's a short question with a long answer. Try to keep up.
I get my Avatars by searching certain shows on the internet. I use
www.google.com . The image search will help you find pictures of whatever character you want (it's very tricky and sometimes you can't find exactly what you want). If the picture doesn't fit in the 64x64 square, you can shrink it down to 64x64 pixels in Photoshop or any other similar program.
that's what I do anyway!
So if you want pictures of Baby Sinclair, try the website
www-thalia.sci.kun.nl/funpage/television/dinosaurs/index.html
then, right click to save the picture to your computer and manipulate the size in photoshop.