It is the idea of Canadian Blogger, Taylor Jones. While sifting through a shoebox of old photographs he happened upon one of his brother sitting in a chair. He looked up to find the same chair in front of him. He grabbed his camera and held the old photo up to the chair until it fit with the background.
Thus began a book deal and another internet sensation!
My personal favorite is the photograph below. The caption reads: "Dear photograph, thank you for everything we had."
It's worth a visit and will send you running to look for photos that just might be worth a submission.