Companies who create and market strong visual characters and objects, like from comic books, movies, TV-series and games and even novels might be able to stop hobbyists from "copying" thier designs, but that won't be a smart move from them: The main reason they produce theese things is to make money, either in direct way through thier product, or through secondary ways, like merchandising or licences for other products. To make money this way, there has to be a strong interest in them in the market. So they need good pr in the public, and a strong fanbase. Stopping people from creating thier own views like 3d models and images and fan stories and the like would only give bad pr and a lot of frustrated former fans. So some might even encourage fans to do thier own thing, as long as it isn't comercial. Such work might even give them new ideas, and happy fans are more willing to shell out more money for products. So most companies might be happy to see fan products, even if they don't admit it.