Pathfinder in "The Martian" split images?

Because this is how Pathfinder takes images. Most of the images you see from the Pathfinder rover are many images stitched together. Some are fairly good stitches like so:

(Even then you can still see artifacts).

Some of them are not so good:

Though the images themselves are usually the same size. Out of universe, it was most likely done because a dozen smaller images shifting around looks better and is easier to see what's going on than if they did four really big images. In universe, you could argue that the team at NASA had pre-cropped some of the images to make it easier to fit in place. In reality, they would probably use an image stitching software and we wouldn't actually see this, but that's not as entertaining.