I suppose the problem we have is how are women to respond to obvious men in the women’s toilets or changing rooms in the moment? Report it to whom? Oh there seems to be no-one here now, where’s your evidence?
As we are frequently reminded, toilets are not policed, it relies on social norms/contract for people to obey the law.
Women are not physically able to stand up to a man in the toilets, or would be ill advised to do so because of the strength/size/power imbalance. We have no recourse if it is our word alone. Hence the photographic evidence option is more open to us.
I agree that it leaves room for mistakes to be made, but the alternatives are paid gatekeepers in every toilet, perhaps CCTV at the entrance, or just allowing men to continue to use our facilities no matter how it makes women feel, and despite it being against the law.
At the time of the offence, women have few practical options available to them.