You're confusing distribution with copyright. Even free flyers or public YouTube videos are copyrighted. If you draw a flyer then I use that flyer as a cover for a book I'm selling, you will likely win in court. (I say likely because it's up to the judge, but there's a lot of case law here.)
> permission you implicitly granted
There is nothing you implicitly grant anyone, except for ownership (which is explicit, because I gave the thing to you).