High resolution images are composed of more pixels than low resolution images. Photos made up of many small pixels generally look smooth and crisp. Those made up of fewer, larger pixels may appear jagged and unclear. However, this does not mean that a photo with a lower dpi (or resolution) is always unusuable. If you plan to use a stock photo in a small size (such as a wallet photo), you can use a photo with a lower resolution and still get a good result.