The pics are called avatars. Go to your profile page (click on the Profile icon at the top right of every page) .... Choose Edit Options on the menu bar. At the bottom of the options page, you'll see Avatar ... click on that, you'll be taken to a page where you can select one of the little cartoon avatars, or you can upload a custom picture from your computer. Note - the picture can be no bigger than 100 x 100 pixels, or 20 kb, whichever is smaller.

Doreen