QR Codes are 2D bar codes that are easily read by smart phones and other devices. These codes easily allow web sites, videos, and other files to be included in a relatively static photo book or other project. Best of all they are low cost or free. These codes can be created on a smart phone or PC. For the iPhone, try QR Code Generator, FancyQR, or Colorful QR. Other applications are available for PC, Android, or the web.
Because QR codes can incorporate any web site or file with an associated url, there is no limit to what can be incorporated into the code. For example, the QR code to the right links to a YouTube video showing my wife heading down a snow-covered slope in an inner tube. I have always liked this video, and now I can easily find it.
QR codes are also amazingly resilient when it comes to damage. For a study comparing the readability of damaged and distorted QR codes, see Wounded QR Codes. In this study, most of the QR codes shown below were readable.