Hi Marsha.
There are indeed several locations in the parks where this type of
green screen photo can be done!
At Hollywood Studios there's a Star Wars photo location inside Tatooine Traders, the shop you exit through after enjoying the Star Tours attraction. Here, individuals or multiple guests can have their image taken in front of a green screen and then super-imposed onto a Star Wars scene. You can view your image on the screens or choose to have an image printed to take with you.
Another great place to create a fantastic 'green screen' souvenir is over at Epcot.
You'll find multiple cameras set up and a huge selection of possible scenes from so many of your favourite Disney movies inside the
Journey Into Imagination pavilion. We visited the pavilion's Imageworks location just last month and I couldn't tear my two kids away from having themselves imaged over and over again, in various silly poses and scenes! It's so much fun and the possibilities at this location are almost endless!
I hope this information helps you out Marsha!
Thanks for visiting the Moms Panel with your great question.
Please write me back any time if I can assist you further!
Wishing you and your family a simply Magical time on your next Walt Disney World vacation!
Kirsten