JPG (just like MPG, MP3) uses what is called a lossy compression format. The incredibly small file sizes are a result of removing 'insignificant' data. Of course, the insignificant data range increases as one tries to increase the compression amount. But you retain full color spectrum unlike GIF which has a limited palette written to the file from which to choose (as DominiqueB notes well). My only advice when using JPG is to retain the original uncompressed image (in BMP, TIF, PNG, PSD or similar) so that you can always adjust the JPG compression later and resave the JPG image. As I said, it's a 'lossy' compression, so once you compress, the 'lost' data is lost for good in the JPG image.

C makes it easy to shoot yourself in the foot. C++ makes it harder, but when you do, you blow your whole leg off.

 -- Bjarne Stroustrup

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