AP - Slice and Reveal

[Dekade]

I am trying to make an illusion on a photo and would like to have some suggestions on how to achieve the effect.

1. I want to simulate a slice/knife cut on a photograph.
2. Then I want to be able to place a separate image or an object in the slice to look like it's emerging out of the slice.
3. The slice can be uniform or un-uniform and can appear as jagged, curved, or straight, etc.
4. One way to describe what I am trying to achieve is to use the example of: a letter pulled halfway out of an envelope.