1. A method for producing a compressed bit-stream from a digital image, comprising the steps of: a) processing the digital image to produce a main subject belief map containing a continuum of belief values relating to the importance of subject and background regions in the image; b) performing a spatio-frequency transformation on the digital image to produce an array of transform coefficients; c) deriving a distortion-weighting factor for each transform coefficient from the belief map; and d) producing a compressed bit stream using an image compression system that is responsive to the distortion-weighting factors.