Since it was predicted that there might be a difference in the effects of compression on different kinds of image, and also in the detail users observe when looking at different kinds of image, it was important to show several different types of image to the subjects.
Four kinds of image were selected: a face, a tree, a map and an interior scene. The second two pictures included several straight lines, whereas the former two were structurally more natural. All of them contained areas of detail and areas of block colour. This combination of image types was deemed to offer a cross section of the kind of images that users would encounter on the Web and also those with differing susceptibility to the JPEG compression algorithm.