The JPEG format is best for color photos.
JPEG stands for Joint Photographic Experts Group. Graphics in JPEG format, or JPEGs, are recommended when images contain many continuous colors. Namely, photos. An example of a JPEG file name would be "climber.jpg."
Photos are typically made up of thousands or even millions of colors. The JPEG format can handle that many colors as well as keep the file size to a minimum. The file size might not be as small as a GIF, but the size is still pretty small compared to other formats.