Assuming this is video, doing an A->B roll, the background quad is the B footage (destination image).

Doing a really realistic page curl without stretching is somewhat hard. You might need to look into cloth simulation systems for that.

Doing cheesy page curl; either roll-up or peel-off; is a matter of sweeping an imaginary rolling pin across the mesh, and rolling/peeling up the vertices that are on the "back" end of that pin, by rotating them around the pin's center axis. This will stretch a bit, but you often don't notice.