That's a myth. Nothing protects online content. If you don't want people to take your images, DO NOT publish them on the web.
Owing to how the Internet works, images are automatically downloaded into the end user's browser cache when they visit your site. It doesn't take a genius to find them. Also anybody can grab a screenshot if they have a mind to.
Disabling right-click is the single WORST thing you can do to your website. It protects nothing. It annoys users by disabling advanced browser navigation features. And it screams AMATEUR SITE! Don't do this.
If you're really serious about protecting content, put it behind password protection. Consider using digital watermarking or barcoding which is invisible to humans. There is a Digimarc plugin for Photoshop described below.