[Inkscape-user] Blending one photo into another.

Before I spend a lot of time trying the impossible:

In Gimp it is possible to take two overlapping bitmap images (like photos) and blend one into the other using a gradient on the topmost bitmap? Inkscape has the ability to blend two vector objects in this manner. But what about bitmaps?

If I vectorize the top image will that make it possible? (Unfortunately vectorized photos often come up huge.)

John Culleton