Sometimes I have an idea for a design that requires, say, three pictures. But as I look through my photos, I can only find two that look good. So I simply use one of the photos twice, but change it up a little bit. In this super simple layout, the first and last photo are one and the same, but the second one is cropped closer up. I put the other photo in the middle to create some contrast.
Another variation you could use, is to print one in color and one in black and white. Then, voila! You have two different pictures to use.
Have a great day!