jpeg or jpg is standard for pictures and have smallest file size, usually used for web but you can print those images too.
JPEG stands for Joint Photographic Expert's Group. It is a processed image format that uses compression to save space.
Joint Photographic Experts Group
http://en.wikipedia.org/wiki/JPEG
Animated JPEG are multiple single jpeg images that is runned under a javascript which runs the jpeg like a animated GIF, by frames of each images.