A photo app that allows you to take pictures while displaying a translucent overlay of another photo.

This would be extremely useful for comparison shots, stop motion, etc. Want to take the same family photo every year? Just overlay last year's photo to get everyone positioned right. Taking pictures of real life locations from a movie? Overlay a still from the movie so your picture can match it. You could toggle the overlay on and off, and even if it was turned on it won't show up in the new photo, but it would be very helpful in a number of situations to be able to do that. This idea is so simple that I feel like it probably exists already but I've never seen it. If it does exist, what is the best app that can do this?