Very briefly, the resolution of an image or picture describes the detail (or information) an image holds. The higher the resolution, the more detail the image has, because there is more information. Information translates to “pixels,” which are the different coloured “dots” that make up an image. The more pixels there are, the more vivid the image is and detailed to the naked eye. If an image has very few pixels the image will appear to be “pixelated”—the pixels look like squares all joined together—but you know exactly what I’m talking about if you’ve ever printed something off the internet (and who hasn’t?).
DPI stands for “dots per square inch.” This is the measurement printing companies use to determine how sharp an image is. Photos or images used for online or web graphics can be at low resolution (72 DPI) and will look FABULOUS on a computer screen. But try to print those same pictures and they’ll look horribly pixelated. For printing purposes images should be 300 DPI or better.
High resolution example:
Low resolution example: