Spot the Difference!

Ok, below is a real brain-teaser that will test your intellect and powers of observation! Are you up for the challenge? It's simple, all you have to do is spot the difference in the two pictures below. Look hard, because you might miss it, but to help you out I'll give you a clue: it's more obvious than you think. Good luck, and make sure you give yourself a big pat on the back if you get it right!