Norman Rockwell paintings completed after 1942 contain an anti-forgery technique that is invisible to the human eye and the eye of a camera. Mr. Rockwell may have learned about Steganography while he served in the US Navy, and created several posters for the Government.
After discharge from the military, he combined knowledge of steganographic principles with his passion for photography. Mr. Rockwell invented a way to hide his name in plain sight.
He created CMYK color paints to match the RGB color model. Because all electronic screens and cameras work on the RGB model, the paints he created could not be seen on an RGB screen or by an RGB camera. The shades of these color models are so close that the difference was undetectable by the human eye. Best of all, pictures taken by RGB model cameras could not capture the difference! Forgers of the day who worked from photographs of artwork would not see any difference when they were producing a forgery.