I get this question a lot, so I try to answer it once and for all.
Commercial use of my stock elements (only those, NOT MY ARTWORK) is allowed. It's free, no payment is needed.
My deviations may NOT be used in any racist, sexist or otherwise demeaning images.
Please use it only in your artwork, selling it without modification as stock is not allowed.
If there is some place where you can give credit, please credit me as "Christoph Struber".
If there is some place for a URL, please use "www.dadrian.com".
If there is no place for credits, you don't have to credit me.
If you use my stock regularly and are happy with it, please consider donating a deviantart core membership.
Why it's free: All the stock I provide here originally made for my own artwork, it was never intended for earning money. SpaceArt is just a hobby for me and I'd like to keep it that way. Also I am a professional artist who needs resources. Often I am restricted by complicated licences. So if you can credit me, great, if not, it's okay as well. Just please don't try to sell my art to your customer as your own. That would be dishonest.