1. A computer-implemented method executed by one or more processors for modifying a digital image of a design to allow blending with an image of a product to represent the appearance of the product when imprinted with the design, comprising: receiving by at least one of the one or more processors a digital design image to be printed onto the product, the digital design image comprising a plurality of pixels each having an associated brightness value and an associated opacity value, generating by at least one of the one or more processors a modified digital design image comprising each of the pixels of the digital design image adjusted such that the opacity value of each pixel in the modified digital design image corresponding to a respective pixel in the digital design image whose associated brightness value corresponds to completely dark is set to a first predetermined opaque value, the opacity value of each pixel in the modified digital design image corresponding to a respective pixel in the digital design image whose associated brightness value corresponds to completely bright is set to a transparent value, and the opacity value of at least some pixels in the modified digital design image corresponding to a respective pixel in the digital design image whose associated brightness value corresponds to a brightness value between completely dark and completely bright is set to a corresponding opacity value dependent on the brightness value of the respective pixel such that the opacity value of at least one pixel whose associated brightness value corresponds to a brightness value that is darker than at least one other pixel is set to an opacity value representing greater opacity than the opacity value of the at least one other pixel.