I thought it'd be sufficient.. I mean, who at the RTA is going to doctor your photo and then try to generate the same MD5 so that they match?
There would be easier ways to doctor the photo, like just.. doctoring it and re-creating both MD5's to match from the fake photo.
Either way it's the same reason digital photos can't be used in court, but since the RTA is one of those cash cows I think they'll either do something really quickly or just appeal and win.