For a "how-to" see the OOF How-To gallery at http://www.pbase.com/ed_k/out_of_frame
I came up with this technique 2-3 years ago when I needed entries for the "altered image" category in the club's competition. I'm not positively disposed to heavy PS manipulation *if* one is entering a photo contest (it's the apples & oranges thing) and so searched for something that retained my basic out-of-camera image while at the same time definitely saying "I've been altered". This is what I came up with and it turned out to be quite successful. More than one judge during the year got up the her seat to look more closely - certain that the part of the photo print that appeared to be a mat was actually a mat. At that point it's "gotch'a" - you almost have to give me a ribbon after being fooled ("story" about illusion images - a two painter challenge. Painter #1 painted grapes so real that birds flew into the painting wanting a bite. Painter #2 - His painting was covered with a white cloth. Painter #1 went to remove the cloth to see what #2 had done - only to discover the cloth was the painting. Had to be there ;>)