Try scanning the above image on the right, and you'll find that it won't scan (as your camera reads the QR code data and sees it doesn't go anywhere).
There are even two types of QR codes, static and dynamic. Static codes will reliable direct you to one website and don't require as many pixels (meaning it'll be easier to scan). Dynamic codes require more pixels but allow you to change the end destination of the code ― changing the end destination allows you to collect individual user analytics and redirect them accordingly. With dynamic QR codes, two different users can scan the same code and be directed to two different sites. Incredible, right?
Interestingly, dozens of "unofficial" QR code variants exist, like JAB codes (which use color and diamond references boxes instead of square ones), IQR codes (somewhat like a rectangular version of square QR codes), and Frame codes (which can be integrated into paintings, backgrounds, and photos to convey information but avoid disrupting the main artwork). If you're interested in learning more about creating these wacky variants, the MATLAB site has an interesting post on the fundamentals of QR algorithms.