1. A computer-implemented method for processing paper forms, comprising: at a computer system, capturing an image of a paper form in which information has been filled-in; extracting from the image a location identifier, which indicates an address in a storage location, external to the computer system, at which a metadata object in a markup language representing the filled-in information is electronically stored; retrieving the metadata object responsively to the location identifier by communication with the storage location via a wide area network (WAN), so as to convey the filled-in information electronically from the storage location to the computer system; and processing the information using a data processing application running on the computer system.