1. A method for locating products of interest using a portable device of a shopper, the method comprising: indicating, via a software user interface presented using the portable device of the shopper, a specific product and a type of related product desired by the shopper; searching a database to identify at least one related product that satisfies the indicated type of related product and that is compatible with the specific product; downloading reference data associated with product packaging of the at least one identified related product, the reference data comprising visual fingerprint data or digital watermark data, the reference data corresponding to artwork of the product packaging; obtaining, from an image sensing device forming part of the portable device, streaming image data indicative of product packaging of a plurality of products; analyzing the streaming image data with respect to the reference data and the at least one identified related product; outputting, by the portable device, a signal responsive to the analysis of the streaming image data; updating, by the image sensing device, the streaming image data as the shopper moves the portable device; analyzing the updated streaming image data with respect to the reference data and the at least one identified related product; outputting, by the portable device, an updated signal responsive to the analysis of the additional streaming image data; wherein, the updated signal is output in a manner that increases its perceptibility by the shopper responsive to the shopper moving the portable device in closer proximity to the at least one identified related product and decreases its perceptibility by the shopper responsive to the shopper moving the portable device further from the at least one identified related product.