You can take any imae off the internet or your hard drive, resize it to 100x100 in a program like Photoshop or Photo Editor, then upload it from your hard drive.
Rather than doing a Google search for "avatar," just go to Google and do an Image search and then in the blank type in what you're looking for. Let's say I want a picture of an VanGogh in my avatar. I can go to Google, switch the tab from WEB search to IMAGE search, then in the search blank type "VanGogh." When I find a pic I like, I right click on the pick and do a "save picture as." Then I open that picture (which I probably saved to my desktop) in Adobe. Once in adobe, I go to image, resize, and change it to 100 x 100 pixels. Then I resave it. The go back to Profile-->options-->change avatar. Then upload that picture from your computer. Voila...