Back before facebook went gigantic people used social networks with avatar like display pics & put up loads of fake data.
It's also much less likely that someone will do it due to the hassle and lack of automation. Though no doubt some hot startup idea is about to be born...
Obviously hijacking an account is illegal, but the means to do it probably aren't: A good number of these 'proves' aren't special, aren't protected documents as far as I can tell. There's nothing illegal about 'forging' a yearbook page.
I'd say these measures are providing nothing but decent ways to hijack an account and have zero legitimate uses as means to identify myself to a random web application.
The same question somewhat applies to government-issued IDs depending on state/country, since many laws regarding falsified IDs only apply to purchasing tobacco/alcohol.
I seriously doubt that the US is going have to have less strict laws regarding forged documents. Just because you think it isn't illegal doesn't mean it actually is.
https://www.facebook.com/help/385569904840341
Facebook accepts any government-issued ID that contains name and date of birth. Examples include:
Birth certificate, Driver’s license, Passport, Marriage certificate, Official name change paperwork, Personal or vehicle insurance card, Non-driver's government ID (ex. disability, SNAP or national ID card), Green card, residence permit or immigration papers, Social Security card, Voter ID card
If you don't have a government-issued ID, Facebook will also accept two of the following items that combined must show name and date of birth. Examples include:
Bank statement, Bus card, Check, Credit card, Employment verification, Library card, Mail, Magazine subscription stub, Medical record, Membership ID (ex. pension card, union membership, working or professional ID), Paycheck stub, Permit, School card, School record, Utility bill, Yearbook photo (actual scan or photograph of the page in your yearbook), Please cover up any personal information we don't need to verify your identity (ex: credit card number, social security number).