JPEG
Joint Photographic Experts Group (JPEG) format image is the most common format used for storing and transmitting photographs on the World Wide Web. It is not as well suited for line drawings and other textual or iconic graphics because its compression method performs badly on these types of images.
JPEG is best on photographs and paintings of realistic scenes with smooth variations of tone and colour. When saving a JPEG you can specify the compression setting with a playoff of image quality to file size, the smaller the file size the more degraded the image.