The copyright issue is one reason I stopped teaching classes from commercial books or patterns. I had to make samples for all those classes, and I wanted to sell the samples afterward. (we're talking about at least 50 samples a year!) Now I just design and draft all the patterns for the classes I teach, and I don't have to worry about it.
It's also hard to decide what is a copyrighted image/design. A flag bargello quilt? I've seen hundreds of them, all different. I could do one without a pattern if I wanted to make one. A colorwash quilt? A French Braid? I borrowed that book from the library and realized that it was just an identical pattern to one I've seen around for years. A baby quilt made in that "Mock Cathedral Windows" style? Fons and Porter have a copyright on it in their magazine. There is at least one website with a copyright on it (older than the F&P magazine). And I learned that pattern 18 years ago at a quilt guild meeting. It's not exactly a new technique, but people can publish patterns for it and claim they hold a copyright, even if it's identical to an older idea.
It's all very complicated... I don't think anyone here plans to steal an idea and profit from it. If you have a quilt that you don't want anyone to copy, however, don't post pictures of it! That's not a legal issue... it's just common sense.