There are two types of images that are commonly used on the web: JPEG and PNG. While each format has its strengths, these two are typically used on the web because they can provide small file sizes that will load quickly when someone is visiting your website. Here is a quick overview of the two file types.
JPEGs allow you to compress large image files down to small sizes. They are ideally used for photographs, complex illustrations, or images with gradients. This format compresses the image, but does not limit the number of colours in the image.
Every time a JPEG is compressed, some of the image information is lost. This means that if you compress the image extensively to make the file really small, you can create a visible loss of quality. Below are examples of a normal JPEG and a highly compressed JPEG.