Those cases do not stand for the proposition you claim they stand for. The Perfect 10 cases stand for the proposition that a website using thumbnails of copyri

Those cases do not stand for the proposition you claim they stand for. The Perfect 10 cases stand for the proposition that a website using thumbnails of copyrighted works may be protected by the fair use doctrine if the creation and distribution of the thumbnails are incidental to a non-infringing purpose (in both Perfect 10 cases, some form of search.) Pinning images in Pinterest is not transformative in any way. Users upload the original copyrighted photos, which are then distributed by Pinterest. In this regard, Pinterest is protected by the DCMA safe harbor, but the users are not. Note that this means that Pinterest would be protected by both the Perfect 10 case law and the statutory DCMA safe harbor, but that users are generally not protected by either. Pinning a copyright photo probably won't get you sued, because lawsuits are expensive. But if you do get sued, the court can impose statutory damages, of at least $750 but up to $150,000 for wilful infringement. Statutory damages are in lieu of actual damages, so the copyright owner does not have to prove economic harm. See 17 USC 504.