Here is an experiment I did using Photoshop to create a reusable and resizable page curl effect. Creating a realistic page curl effect can be quite complicated due to the shadows and masking involved, so the idea was to allow simple pasting of a source image with as little adjustment as possible to achieve the finished effect. If your source image is larger than the standard one you will need to adjust the main vector mask to the left and bottom (both straight lines requiring simple select and drag). And that's it.

Artwork by Cristoph Niemann (yellow) & Jonathan Mak (red).