1. A computer-implemented method for generating a blended product image comprising retaining a digital image of a product, receiving a digital design image to be printed onto the product, generating a blended digital product image by adjusting the opacity value of each pixel in the design image such that completely dark pixels are substantially opaque, completely bright pixels are substantially transparent, and the opacity values of at least some pixels having brightness values between completely dark and completely bright vary according to the brightness value of the pixel.