If you're a collage artist--or a card artist hoping to have work published somewhere--you may already have plenty of anxiety about copyright law. If not, you can work yourself up into a snit by following the blog of Tammy L. Browning-Smith, artsandcraftslaw.
The blog is full of useful information, focused on intellectual property and the arts-and-crafts industry. The writing is friendly and down-to-earth--easy for us laypeople to understand.
The subject matter is uncomfortable, which is all the more reason to pay attention to it. Even if you use only images produced by angel companies, even if you don't expect your work ever to be reproduced mechanically, you probably need to know a bit about copyright law. Browning-Smith's blog is a good way to inform yourself. Go see.