How to make an image fade to transparency in Gimp?

Question

Graphic arts

How to make a smooth transition to transparency in Gimp like
this

Answer 1

1) drawing a frame with a shadow
2) a mask in the form of a gradient on this layer.

Answer 2

And for absolutely geeky perverts, you can play with the transparency parameter of the eraser (this is if your goal is not to sculpt frames, but, for example, to overlay pictures)