Done on Disc 1 Episode 4 (Siblings) chapter 3.
There are 20 crayons to find in this chapter. When you see them it tells you to point and say "Picture".
Tip: You don't have to point to get the pictures to take. Any loud noise will do. I played music very loud and put the kinect in front of the speaker. This work 99% of the time. Best if you pony up and watch it and yell something so it will take the pictures.Even if you miss one you can go back and get it later. Once to get the last one you need you can skip to the end of the episode!
I miss one at the start, then finished it. Went back and got the one I needed then skipped to the end and got the achievement.