Emphasis
Emphasis means putting stress on a word or a group of words to give them more importance. Emphasis gives certain elements greater importance, significance, or stress than other elements in the text, which can guide your reading of the text as a whole.
This image is an example of emphasis because the camera is focused on the apple while the background is a little more blurred. You can also see that the red is an emphasis of color when compared to the brown of the deck. It is obvious that the apple is of the most importance in this text. This is also a great example of color use or contrast.
In this example the emphasis is on the two people riding horses in the field. This is apparent because the image in the knothole is much clearer than that of the wood in the foreground. The knothole also works as a frame that directs the eye to the people riding horses.