JPEG
From GDWiki
JPEG or JPG is a lossy image file format that fools the human eye by disregarding insignificant image data. JPEG's are not ideal for games. Although the compression algorithm is very powerful, an uncompressed image will contain compression artifacts. These artifacts may blend in nicely into any real-life photograph, but are hideous in a computer-generated picture. JPEG does not support transparency, and it is inadvisible to force it. If the image uses a particular color like hot pink for transparency, there will be small variations in the hot pink, and most of the original hot pink image will not be transparent.
