I received an invite to the Vidoop Beta, so signed up for an account.
The sequence by which you pick your image grid is pretty slick. Below are the categories I chose (completely randomly I assure you)
Once categories are chosen, they help you practice
before eventually presenting you with a real grid to authenticate with
My tests indicate that the order of the characters for the code doesn't matter, e.g. 'AGB' is as good as 'GAB' in the above. Not sure why.