What face would you like to present to the world? You can choose almost any photo as your Gmail picture, to show up whenever another user rolls over your name in their inbox, Contacts, Chat list, or when someone looks at your public Google Profile.
You can select whether you’d like all Gmail users to see your picture, or only those who you’ve allowed to chat with you, using the radio buttons next to your uploaded photo on your Settings page.
Once you apply your picture, you’ll be able to view and change it from your Gmail settings page, and other users will see your selection when they roll over your name in conversations or in their contact lists. It will also show up as your picture in Google Talk. Likewise, picture selections made in Google Talk will be reflected in your Gmail interface, though there might be a slight delay for the change to take effect. If you have a Google Profile, changes made to your Gmail picture will be reflected in your Google Profile. [source]