This will most likely be the second achievement you get.
After you've scanned yourself in for the above achievement, you can choose one of six Pixar worlds, choosing from Ratatouille, The Incredibles, Toy Story, Cars, Up, and Pixar Park. Choose one, clap your hands (Make sure you actually make the sound, i.e. make contact. Don't just mime clapping - Thanks HyruleBalverine & Z3RO 37), and pose for three seconds for the picture. This should be done simultaneously with the following achievement, which will pop when you have shared to your www.kinectshare.com friend feed.