The law is quite clear on this. You're granting Instagram a license to display the image, so they are allowed to do that. Other websites aren't, unless you grant them a license, too.
So the foot fetish website is infringing copyright. And the author of the image can sue them for damages.
They can also ask ISPs to blacklist the page if they don't comply.
Kind of all the stuff that the MPAA does when they find a movie rip on someone's server, the photographer could do here, too.
What you say is right, but is about copyright, not consent.
No social media collect the consent of people in the actual pictures when the person in the picture is not the one who is posting it.
So the foot fetish website is infringing copyright. And the author of the image can sue them for damages.
They can also ask ISPs to blacklist the page if they don't comply.
Kind of all the stuff that the MPAA does when they find a movie rip on someone's server, the photographer could do here, too.