from the view it looks like her though not sure 100%,
also point is why is she keeping such pics in her phone
how can you tell its her by just looking at the pussy?? or have you seen the pussy irl before?? or the pic you posted is cropped??
I would say that you should first try to record her nudes maybe like when she is having a shower and confirm if its her.
and as for the reason of the pics maybe she sends them someone or simply its just your father or her boyfriend, try to check her messages and find if she sent them to anyone, check when the pic was taken and even the folder it was in can tell a few things like if it is camera folder its taken by her but if in downloads its an internet pic or in a folder of any social media somebody might have sent it to her