1. A method comprising the acts: receiving first and second image data corresponding to first and second image frames both captured by a first camera of a point of sale system in a retail store, the point of sale system being able to recognize an item from the first image frame but not being able to recognize an item from the second image; recognizing the item from the first image frame, and determining a GTIN (Global Trade Item Number) identifier corresponding thereto; and using backpropagation, adjusting weights in a multi-layer neural network that includes plural convolutional layers and max-pooling layers, topped by plural classification layers, the adjusted weights causing the network to respond to presentation of the second image data at its input by outputting the GTIN determined from the first image data.