Update for ALL versions of Chrome
The flag has been changed for this feature once again. To enable this on all versions of Chrome copy and paste the following into your Chrome Omnibox (address bar)
chrome://flags/#enable-google-profile-info
hit enter and select enable. Now restart Chrome and your avatar will have changed to your Google profile pic.
Originally you needed to have two or more Chrome profiles activated but with this new flag this is no longer the case; the image can be seen with just one Chrome profile.
The information below is pretty much defunct in the more recent versions of Chrome. Please use the details above to enable Chrome to show your Google profile image.
Some time ago it was possible to use your Google profile picture as your Chrome Avatar, unfortunately this feature was removed and you were stuck with the default avatars that Google allows you to choose from.
It is now possible to use your Google profile picture again by launching Chromium or Canary with the following switch:
--gaia-profile-info
To launch with these switches on OS X you would open Terminal and enter the following for Chromium:
/Applications/Chromium.app/Contents/MacOS/Chromium --gaia-profile-info
And the following for Canary:
/Applications/Google\ Chrome\ Canary.app/Contents/MacOS/Google\ Chrome\ Canary --gaia-profile-info
Once you have done this you should now see your Google picture instead of the avatar you were previously using (as long as you are signed in of course).
After launching once with the command line switch it is not necessary to repeat the process.
Windows users I am not sure how you launch with switches but I think it has something to do with right click, select properties and then....sorry, you will have to find out yourself. A search for 'launch Chrome with switches' in Google should be able to help.