display | more...
The JPEG image format is best used to compress 24 bit color images with a smooth gradient. Sources of such images would include scanners, digital cameras, and high quality image renders that uses a method such as ray tracing or other methods that produce realistic looking images.

JPEG handles things such as sharp lines and sudden color changes very poorly. An image containing these will compress poorly and will have a large number of JPEG artifacts. If the image also has very few colors, it would have been better off as a gif.

JPEG is one of the three accepted formats for world wide web images. (Other formats work too, but these are the most well supported.)