Juxtaposition is the placing of contrasting objects in the image, to emphasize the difference. Juxtaposition creates an interesting story behind the image.
The images above are examples of juxtaposition. The first image shows a line of traffic, contrasting with one person on an empty road. The other two images show old structures, contrasting with new, modern buildings. 'Dear Photograph' is a website with many photos conveying juxtaposition. In these images, people take an old photo, taking it back to the place it was taken, and lining it up with the background, showing the contrast between the past and the present, telling a story about the old photos.