1. A flatbed scanner comprising: a platen for supporting a substrate, said substrate having a surface bearing a pre-printed graphic image; a carriage for traversing across the surface, said carriage comprising: a pagewidth scanhead for scanning the pre-printed graphic image during a traverse of the surface; and a pagewidth printhead for printing a position-coding pattern onto said surface during said traverse, said position-coding pattern identifying an impression identity and a plurality of positions; an ink supply containing an ink for printing the position-coding pattern; and a processor configured for generating association data, said association data indicating an association between a scanned graphic image, the impression identity and the plurality of positions, wherein said impression identity is initially unassociated with said pre-printed graphic image.