Most people are used to seeing photos, especially portrait shots, from a straight-on viewpoint. In other words, the subject is looking directly into the lens and is positioned directly in the middle of the shot. But, good photographers know how to take shots from a variety of viewpoints. For example, positioning a tree in shadow in the left third of the shot has more power when the viewer sees it, precisely because it's less traditional. It draws the eye into the shot and is good use of what is called the rule of thirds. Also, consider that an element in a particular photo may be more interesting to the eye when it is positioned in the upper right position of the shot or the top third. You don't have to be a skilled photographer to buy quality stock photos, but keeping some of these basic tenets in mind will help you choose more powerful images for your presentation.