It's not my idea. This guy has done many, and even written a nice tutorial for you -- which is great if you have photoshop. (tutorial link is at the bottom of his webpage)
As you probably know, Photoshop is expensive if you don't have it, and very dense and hard to learn, if you do have it. It's probably a wonderful tool, but just reading through the tutorial was enough to make me shiver (and not in a nice way).
So, here's a guide to making your very own Invisibilia to print, frame or whatever... using just the drawing tools you can find in an ordinary word processor, or in this case, PowerPoint 2007. (hey, you may know many of these tricks already. But I bet you learn at least one new thing. :-)
Ready? Let's go.
Step 1: Start PowerPoint
So, open PowerPoint with a blank document. I always immediately click and delete the default text boxes that are provided (so generously!).
Find the tool for Inserting a Photo.
Insert your photo and resize it to fill up the whole "slide". You may also want to do some cropping at this time.