In one arrangement, retail product packaging is digitally watermarked over most of its extent to allow machine identification by one or more inexpensive cameras at retail checkouts. Such a system also considers image fingerprints, product configuration, barcodes and other available information in identifying products. Imagery captured by conventional or plenoptic cameras is processed to derive several perspective-transformed views, which are provided to the identification system—increasing throughput by minimizing the need to manually reposition items for identification. Crinkles and other deformations in product packaging are optically sensed, allowing the surface to be virtually flattened to aid identification. A marked conveyor belt at the checkout station increases speed and accuracy, and provides other benefits to both shoppers and sellers. A great variety of other features are also detailed.