It’s not much different than a profile picture on most social media networks, is it? You could have done all of this with your Lemmy profile picture as well.
Phones are a bit more ubiquitous for older folks though. Imagine a vulnerability that allows me to post my “pic” as pulling from your phone and it comes up with a picture of your cousin or something. Or if I’m targeting you, you’re an old person that doesn’t understand technology and you see your granddaughter show up in the picture and don’t look at the number or anything. There seems to be a lot of ways this can be abused. I hope I’m wrong and we’ll never see a story about people abusing it, but people pretty much always abuse these things.