Abstract: A method of authenticating products or packaging by analyzing key ingredients on products or on product packaging is disclosed. Light-sensitive compounds can be used to identify the product or product packaging. The product or product package may include visible or invisible ink containing a particular light-sensitive compound. One or more light-sensitive compounds and ink, if used, may be printed in one or more locations on the product or product packaging to produce an authentication mark to inhibit inadvertent or intentional removal of the mark, thereby rendering the mark tamper-resistant. The mark is sealed to isolate the mark from the environment. A device may be used to irradiate the mark and read light absorption or emission. A controller determines the authenticity of the mark by comparing the emitted or absorbed properties to a standard.