It means don't steal my images.
It was designed to protect work that is intangible: it's illegal to steal a book, and copyright makes it illegal to steal the content and make your own book. That would be tantamount to stealing the book in the first place. The problem with copyright is that it's abused by corporations who buy and transfer the rights to a work for someone who is often deceased. That's why some people argue that copyrights should be abolished, but they miss the original intent: to allow individuals to earn a living making creative works, and to encourage the production of those works. If you listen to music, watch TV or movies, enjoy fine art, novels, newspapers or most of what's on the internet, it's because copyright made it possible for someone to spend their time perfecting their craft.
I check. It's not hard to find out who's using my work. Don't be one of those people.