Google Earth can be a great tool for observing satellite photo patterns. In version 4, one can see patches of images that are clipped together. Since a satellite cannot
take a picture of the entire world in one shot (why not?), they have to stich together multiple images.
If you have Google Earth, you can use
this Google earth .kmz file to find one location where three photos meet. Zoom in and out to see different patterns.
Then look at your local region and look for patched photos.
If you don't have Google Earth, you can
download it here. I used version 4 (a beta release in June 2006),
I don't know what this will look like in older versions.