The fundamental question that needs answering is: should we actually prevent minors below the age of X from accessing social media site Y? Is the harm done significant enough to warrant providing parents with a technical solution for giving them control over which sites their X-aged child signs up, and a solution that like actually works? Obviously pinky-swear "over 13?" checkboxes don't work, so this currently does not exist.
You can work through robustness issues like the one you bring up (photo uploading may not be a good method), we can discuss privacy trade-offs like adults without pretending this is the first time we legitimately need to make a privacy-functionality or privacy-societal need trade-off, etc. Heck, you can come up with various methods where not much privacy needs trading off, something pseudonymous and/or cryptographic and/or legislated OS-level device flags checked on signup and login.
But it makes no sense to jump to the minutiae without addressing the fundamental question.
You can work through robustness issues like the one you bring up (photo uploading may not be a good method), we can discuss privacy trade-offs like adults without pretending this is the first time we legitimately need to make a privacy-functionality or privacy-societal need trade-off, etc. Heck, you can come up with various methods where not much privacy needs trading off, something pseudonymous and/or cryptographic and/or legislated OS-level device flags checked on signup and login.
But it makes no sense to jump to the minutiae without addressing the fundamental question.