I have had this concept in mind for a long time, and had taken some of the elements in preparation for the main event, the appearance of the Super Moon in March of 2011.
The first shot was of the bird, on the beach in Puerto Vallarta in 2004, taken with my deceased Canon EOS 20D. The second image was the tree, taken with my Canon G12 in 2011 while I shot Mt. Rainier with my other camera. The third was the Super Moon, shot with the Canon EOS 5D2.
For the bird and the tree, I used the color selector to capture just the subject and popped it onto a new layer using Control-J, then copied that and pasted as a layer on the SuperMoon image. I had to do some scaling to get things to come out right. On the tree I was fortunate that the edges of the branches appeared illuminated by the color selection process - the result of pure dumb luck.
Here is the finished image:
You can see the full size image here.
Canon EOS 5D Mark II
Canon EF 100-400mm f/4.5-5.6L IS USM