That photo was a pretty dick move. But then again, would it even work? Once the prosecutor became aware of her exceedingly extensive hobby, her claim of that photo being evidence of anything would be questionable. In the first place, it's a photo taken with her own phone, in the selfie mode, so all things considered, it automatically looks more staged than security camera footage or a photo taken by someone else. It's just that the intention of using it against Sawatari is malicious in itself and shows a complete lack of trust. This right after he promised he won't tell anyone and they even had that fulfilling discussion about the hobby they both love.