Is this stuff legal?
It’s hard to know where to start with the potential for copyright infringement when considering 3D printing. Whether it’s infringing on a rights holder’s image, copying another person’s model, or mashing up existing work, it’s all easy to see on the leading model repositories.
As things stand, these sites work in the same way as the likes of YouTube, but in a less automated way. Anyone with a claim can send a takedown notice to the likes of Thingiverse, which will be acted on accordingly (and it’s these sites, and their users, that are likely to be liable, rather than the printer makers themselves). Most online communities police themselves though, and attribution is often enough to satisfy a fellow model maker.
And as for major rights holders? Well, judging by all the Star Wars models out there, there seems to be a watching brief from them. But that could change at a moment’s notice so always be aware of what you’re printing something for.