Cropping is used to remove the unwanted portions of an image. It also can be used to straighten images. But most commonly it is used to enhance the composition of a photograph. Let’s look at this image of a waterfall. The stream looks tiny in comparison to the canyon it has eroded. This view makes the stream look like a straight downstream flow. But a closer look reveals that it has an interesting curvature. To enhance the composition I select the crop tool from the tool bar by clicking on it.
Now the image’s composition has been improved by making the stream more prominent and its curvature more apparent.