<human>: My girlfriend of six months recently received a facebook message from an obviously fake account (no friends, no photo, etc...). The message contained nothing but a nude photograph of her that she had taken about two years ago in a previous relationship. 

The photo does not show her face but she knows that it is her and she knows that there are more photographs from the same relationship, many of which do contain her face. She received the message two days ago and she has not responded and the sender has not written anything else since.

She contacted her ex boyfriend, who she knows had the photographs on his computer, and he of course swears that he never shared the photos with anyone. So we have no idea who is sending these photos, and we do not really know what to do now. 

Should we continue to ignore the message or should we engage the anonymous sender and try to figure out what they want? Should we report the fake account on Facebook? Is there some way to track down the person that is sending these? My GF feels super vulnerable and I just want to be able to help in whatever way that I can. Thanks reddit!!

Could you distill the essence of the text into 1-3 sentences?
<bot>: My gf is receiving old nude photos of her from an anonymous sender on facebook. We don't know what to do.