~Codenine
Thx for the fading comment, but its easy, heres a tutorial.
1:Get some-sorta background.
2: Get a render/image.
3: Put the background and image are in seperate layers.
4: Select the image and go: Layers>Add Layer Mask>Hide All
5: Select the gradient tool and it will be set to: White-Transparent.
6: Use the gradient tool over where the image was maked, and part of it will show depending on how long the gradient is placed, and where.