Guess 25 pictures I got 25 out of 25*
If you visit the OS you will find the proper quiz where you can record your responses. You get 7 minutes to guess all 25 correct and if you fail, they will give you the answers at the end.
Although, I'm pretty sure the order they give you the answers in is wrong.
*Please don't ask me for any tips or clues as I believe in fair play.