Creating a split screen to view two images at once

Actually, you can do this in iPhoto. First, select the multiple photos that you want to view (by holding down the "Command" key as you select each one). Then double-click on one of the photos. All of the photos that you selected will then be shown together in one viewing window.

This is not a feature offered by iPhoto.

iPhoto menu -> Provide iPhoto Feedback for feature requests.

If you want to compare an edited version with an original simply tap the shift key. This will work if the pic has been edited with iPhoto, only.

Regards

TD