1. A method of recording an input image as digital data, comprising: determining input bounding boxes corresponding to objects in the input image; comparing data describing the input bounding boxes to data describing a set of reference bounding boxes; for an input bounding box sufficiently similar to a reference bounding box, comparing objects in the input bounding box and the reference bounding box; and if the object in the input bounding box is sufficiently similar to the object in the reference bounding box, coding the object in the input bounding box using a pointer to the object in the reference bounding box.