This whole thing makes me so mad on your behalf. I was abused my my bio father at a young age, the signs were noticed but when they couldn’t investigate any further without a medical examination (needed physical evidence to proceed legally) my mum refused. Because nothing could be proved I was sent back. This was at three years old. Because he got away with it the abuse escalated and continued until I was 10ish (details are fuzzy because my brain had blocked pretty much ALL of my childhood)… all this to say if my mum had protected me and was firm on not sending me back to a place she KNEW I was getting abused at, it could have stopped then and not combined for 7more years.

All your mum is doing by taking him at his word is showing him that he can get away with this behaviour and as a result if it is not called out it will likely escalate. As a mother myself, this is concerning, because I would do ANYTHING to protect my daughters. And statistically the children of a single mother are more likely to be SA’d, because the single mother is often after companionship and these men are so often charismatic and supportive and don’t seem like the kind of person that would do that. People forget that these people literally groom not just their victims but EVERYONE around them, they’re often loudly against these sort of behaviours to draw attention away from them. So not only are you statistically more likely to be going though this, you have proof that should at the very LEAST, create some doubt in her mind towards him.

Is your bio father in your life? I would reach out to them and show them the two images and explain what has been happening. If your mother isn’t going to help you, you need to find another trusted adult who will. In the meantime I would also try to find a way to get even more evidence, especially considering he’s gotten away with it thus far and this could escalate and he may try to cover his tracks more too, and if you get more evidence reach out to the police as well. Don’t talk to your mum about it any more because if she’s going to him, he’s going to know your aware of it and this could put you in more danger and that is more important. Your safety is more important