1. A method for use in managing delivery of content over a network, comprising: receiving a message, wherein the message includes an image file; extracting the image file from the message; generating a signature vector from the image file, wherein the signature vector includes at least low frequency bits and intensity bits determined from the image file; determining a weighting vector using a machine learning mechanism on a plurality of known other image files; performing a weighted min-hash near duplicate detection (NDD) using the weighting vector to determine if the signature vector indicates that the image file is likely to be a spam image; and based on a result of the weighted min-hash NDD, selectively blocking the image file from being delivered to a destination.