Absolutely loved this lesson. It was so much fun.
For my class I added an extra incentive. My class is divided into groups and so I gave each team 100points and told them they had to bet on each picture. They were given two flashcards, one saying 'FAKE' and the other 'REAL'. If they got it correct got the amount they bet on it, if not they lost it.
I've used it on low-level, high-level, 1st, 2nd and 3rd and it has been fantastic...
I have added the FAKE REAL documents to this thread...
Great fun!