That's actually a very real problem that mega money has been spent on. The same legal problem appears on sites like YouTube around fair use and copyright. In terms of fair use that doesn't apply here see:
https://softwareengineering.stackexchange.com/questions/1217...
Regardless platforms are partially responsible for the content that their users upload into them. Most try to absolve themselves of this responsibility with their terms of service but legally that's just not possible.
Personally I'm an advocate for fair use but I'm also an advocate for strong copyright laws and their enforcement. In the short time the internet has been available to most people in the world there is a habit of stealing others work and claiming it as your own. Quite often this is for some financial gain.