1. A coder for an object-oriented video system, the coder comprising (a) Input image means for receiving a sequence of input images, together defining a moving image, for coding; (b) An object separator arranged to separate out from the moving image a foreground object and a background object, the background object being relatively motionless with respect to the foreground object, the object separator utilizing (i) a potential background store, within which is built up, over a plurality of input images a potential background, and (ii) an accepted background store within which is stored at least some parts of the potential background which have persisted for a desired period; and (c) A block coder arranged to code and classify blocks of the image and to produce an output date stream for storage or onward transmission, each coded block within the data stream being identified as relating either to the foreground or to the background object.