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.

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.

There are free tools for anyone to try and find if someone has copied their material. CopyScape takes Google searches a step further to find sites using your text. Tineye does the same for 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.

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.