Showing Scale
In this assignment we were to take two pictures, 1 picture of something that is hard to see its true size and then another picture of another object showing the scale of the first pictures subject.
When the size is important in a subject, you have to show scale, because it gives the sense of the actual size of the photo. The photo on the left is using scale because you get a sense of the real size of the subject, but in the picture on the right, the subject looks bigger than it really is.