Ink-based technologies are typically used for product authentication, but they may also be used for identification and tracking if a unique product identification code is included in the marking. Most of these technologies are inexpensive and relatively easy to apply. They are very effective and are most commonly used to authenticate paper products, such as paper valuables and documents.  There are several different types of ink that can be used to mark products for anti-counterfeiting purposes. They may be distinguished by their: 

* reaction to chemicals 
* reading procedure 
* reading tool 
* specific characteristics.
Anti-counterfeiting inks may also be visible or invisible. Invisible inks are used to: 
* avoid altering the appearance of the product 
* avoid interference with subsequent product processing 
* prevent easy detection by potential counterfeiters