Oh come on!
If we are talking about freaks and perverts ANY picture you post on the internet is potential fap material. That family Christmas photo? Fap material! That cute picture with your dog? Fap material! That otherwise completely normal selfie you took? Fap material!
There are all sorts of demented people out there and it's best not to think about what even your most innocent or benign photos are being used for.
And from what I understand foot fetishists are quite particular in their tastes so what you see as your perfectly normal feet might be completely uninteresting or even revolting to a foot fetishist