Image formatting

JPEG:
(Joint Photographic Experts Group)
This format is a way or flattening image files and compressing them, the main downside unfortionetly is the quality loss, although they can contain a very large amount of colours. The colour code is Bitmap wich is an image created with bits, the number of bits determined on the availiable colours.

PSD:
(Photoshop Document)
This is the format that  is used when you edit in photoshop, it is also the default format you would save your image in to keep the layers. It is accepted by many other programs and internet image banks. PSD's also can use any colour code (RGB, CYMK, Greyscale etc.).

BMP:
(Bitmap)
This is a format for raster images, made by Microsoft Windows. It uses colour and B&W images, another advantage is that it is supported by a very wide range of software.

TIF:
(Tagged Image File Format)
Popular with Macintosh users, it is a very flexible image format. it doesn't compress at all and looses no quality. The downside is that, because of this, the file is normally farely large.

Site:
http://www.image-formats.com/
http://www.coolutils.com/Formats/PSD