I looked up some other definitions. On http://sceneinadifferentlight.com/outer-banks/juxtaposition, Dan Waters defines juxtaposition thus: "An act or instance of placing close together or side by side, especially for comparison or contrast", a slightly more restricted definition.
Other definitions were more or less on the same lines, the emphasis being on relationship between the elements as the most defining characteristic. This ground was covered in Relationship between Points in Chapter two and one of the images used in that exercise is particularly relevant here:
There is a clear relationship between the golfer's ball and the hole, the golfer's aim is to juxtapose the two as closely as possible.
I took an image demonstrating a more subtle juxtaposition in Kiev:
This was taken during a rainstorm, converted to black and white using Silver Efex Pro2 and the colours replaced in the chair using the Brush Tool. I considered it important that the chair stands out and resaturating it was a straightforward solution.
The relationship is between the empty chair and the rain - the chair was actually used by a self appointed taxi organiser who ran for cover once the rain started. I think it is important the chair faces the road to the left, so clearly has a function of pointing towards oncoming traffic yet is vacant on account of the weather.
Although the exercise brief was for one image only, I add another one below:
This shot was taken in Polperro on the day of some Morris dancing. I captured the relationship between the dancers and the flautist by composing an image that showed the dancers as a reflection in his sunglasses.
