It seems like that is very relaxant information that was not considered by the court. If this was a cryptographic hash I would say with high confidence that this is the same image and so Google examined it - there is a small chance that some unrelated file (which might not even be a picture) matches but odds are the universe will end before that happens and so the courts can consider it the same image for search purposes. However because there are many false positive cases there is reasonable odds that the image is legal and so a higher standard for search is needed - a warrant.