I recall seeing a paper a while back for an algorithm that could automatically and seamlessly "graft" texture from parts of an image onto another part of an image.
The approach was something along the lines of the following:
You'd build up a databases of small squares of pixels (perhaps 8X8) from the parts of the picture that are present.
You'd then pick an empty pixel (the "destination" for the texture graft) to fill in, and look for one of the squares in your database that most closely matches the surrounding pixels. You'd then color the empty pixel according to the color of the corresponding pixel in the square you find. Then you pick another empty pixel and repeat until there are no empty pixels remaining.
Of course, this is only a vague description because I can't find any references to this algorithm to refresh my memory of the details! Can anyone help?