Can Photoshop extract similar content from two dissimilar images?

Question

I have two fairly different image files, except for a single element in the photo. Is there a procedure that can be done in Photoshop (or any other app, for that matter) to extract a mask for that element? When applied, I'd like that mask to remove the background, such that the resulting image (with transparency) can be re-used elsewhere.

I can arrange one over top of the other, change the upper layer's Blending Mode to Difference, then line up the pieces and see my target appear as a black area, but that doesn't seem to get me all the way there.

Answer 1

There's nothing that would do that automatically and yield satisfactory results, but you could get most of the way there with a series of channel calculations.

http://help.adobe.com/en_US/Photoshop/11.0/WSFC798FF0-F7E7-4792-814D-808CCC1DCBD3a.html