Tamriel Rebuilt is based on source material copyrighted by Bethesda Softworks. Since Bethesda and their parent companies have not officially given us the rights to The Elder Scrolls, what we are doing is subject to the usage agreements of Morrowind's End User License Agreement. Technically, Bethesda could step in at any time and demand we stop this project or release their own version of Tamriel Rebuilt.
Similarly, all user-created assets are copyrighted by the individual modders who made them. Since you (hopefully) want to contribute to Tamriel Rebuilt we need to talk about copyright and how it affects you.
Disclaimer: Tamriel Rebuilt and its members are not qualified to give legal advice. Seek a copyright lawyer if you need actual legal advice.
As a modder, you're making assets for us, which includes things like models, textures, concepts, interior and exterior cells, and also includes lore ideas, quests, names, and dialogue.
What TR can do with your assets
When you create assets for us, you are allowing Tamriel Rebuilt to use those assets (or not) anytime, anywhere, even if you leave the project. We can also edit, modify, or remove your assets to suit our needs. TR assets may eventually be released as a Morrowind modder's resource.
What you can do with your assets
You still retain as much control over your creations as copyright allows; you're welcome to use that work elsewhere as you please, such as in another mod or your portfolio.
What Bethesda can do with your assets
Bethesda owns the Elder Scrolls, and everything to do with it. Similarly, when you agreed to Morrowind's End User License Agreement you gave Bethesda the rights to use and redistribute anything you made using the Construction Set. You might not get credit or get paid for this, nor can you say "no".
Also, during the creation of assets for TR, you might end up using stuff copyrighted by Bethesda. This includes anything lifted from the vanilla game, ranging from textures to lore. Because of this, Bethesda can claim ownership of it or at least force you to remove your creation from whatever it's being used in. In particular, if you want to use the things you made for TR in another project not related to Morrowind, make sure you remove all assets that were not completely made by you.