Follow the dots...
I’ve tested my recently purchased a Nikon Coolpix S5 compact digital camera. I’ve played with the Macro /Close Up feature and for testing I took a photo of a printout (done on a HP Color Laserjet 3700).
To my astonishment, the photo cleary shows the “yellow dots”. As you may know, most color printer manufactures print a forensic watermark on each sheet of paper a printer creates. This behavior is found in most color laser printers, despite there is no law mandating this feature.
The encoding used is undocumented, but has been cracked for Xerox printers last year. It includes at least model, serial number and date of the printout. In other words, every piece of paper created can be clearly linked to an individual printer. Useful for law enforcement agencies, but really scary when abused.
Note: some very recent and high-end printers do no longer produce those yellow dots, and some believe an even more sophisticated scheme of forensic watermarking is used in these devices.