I always say... at the end of the day, if it makes you happy thinking and believing she's ticklish and this is a picture of her being tickled, then why not? Believe what you want to believe if it makes you happy.
At the end of the day it doesn't really matter. None of us will probably ever get the chance to ask Angelina if she's ticklish, nor will any of us ever get the chance to tickle her, so who cares? Life is short. Believe what makes you happy.
For me personally, it could be 50/50. Due to the angle and placement of the fingers it could be a tickle, but who knows. They are all smiling and laughing about God knows what, so who really knows.