Well... no. Sorry, it doesn't work that way. In fact, it's the opposite. If someone publishes material on their website, it is automatically protected by copyright law.
You can read more than you ever wanted to know about this stuff at Wikipedia or the US Copyright Office, but the bottom line is that if you didn't develop the text, draw the image, or take the photo yourself, then you must have the OK from whoever owns that material.
Just as the English teacher could always tell somehow when a report was taken mostly from some reference source, it isn't necessary for someone to stumble across a site using "borrowed" text or images.
In addition to these and many other similar free services, most such sites offer a paid service which will keep constant watch for anyone using their clients' content without permission.
The Bounty Hunter is Hungry!
In addition, there are companies that make their money by finding those using text or images without permission, then going after the violator for payment. These "bounty hunters" keep a percentage of whatever they can get.