Copyright and license rights are really complicated. In every country of the earth the interpretation differs and as normal internet user one is quickly overwhelmed with the possibilities, but also with the obligations.
Those who upload something to common and mostly commercial platforms have agreed to the terms of use that all files are published under a special license. Those who didn't read the terms of use don't know about that which is why it seems to simple. In fact one cedes all rights on the file when uploading a photo. Such a nasty interaction should not happen in Stud.IP! Those who upload learning materials here shall continue to have the full control over the use of their own files.
We don't get around a license on the learning marketplace. And we also don't want illegal wheeling and dealing. We assume that all those that provide a file freely on the marketplace also want that the file is used in the end and that it may be used. Therefore the following rules apply:
Fortunately there are smart people that have made clever thoughts regarding licenses. Therefore the so-called CreativeCommons licenses exist. These are valid internationally and mean that which is required above. Thereby, everyone that is using the marketplace has legal certainty. These licenses are used very often outside of the marketplace. Musicians license their raw music files with them, writers their poems and lecturers naturally their slides. The only real requirement is that the authors of the learning materials must be named transparently in one form or another in case of distribution or modification!
This is a little warning: If you intend to gain millions of euros with your slides or exercise sheets and sample solutions, do not put these learning materials on the marketplace, since the use of all learning materials is free of charge (of course we also do not gain money with it) and the learning materials can be distributed at will once they have been downloaded. There is a CreativeCommons license that excludes commercial use. That license is impractical for the marketplace. Ask yourself this question: When lecturers use learning materials from the marketplace in their courses and project for example an information chart from a presentation onto a wall, would it be a commercial use? Yes, somehow, because they are paid for their work as lecturer. We put emphasis on legal certainty for all users. Therefore no learning materials are placed on our marketplace that exclude commercial use. Nonetheless you still have all the rights to publish your slides via another way using a publisher and get royalties.
Basically you can always do with learning materials in the marketplace: