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.