This will surely only work if the person in the photos has a copy of the photos to upload to create the hashes and that the posting the 'revenge porn' does not alter images in any way.
Even sophisticated filtering software can be by passed by rotating the image through a few degrees, altering the contrast/brightness or cropping then adding a patterned border etc.
This sounds more like a PR campaign than something that is really going to stop a person determined to cause someone distress by upload images.
