Anti-counterfeiting measures

Traditionally, anti-counterfeiting measures involved including fine detail with raised intaglio printing on bills which would allow non-experts to easily spot forgeries. On coins, milled or reeded (marked with parallel grooves) edges are used to show that none of the valuable metal has been scraped off.

This detects the shaving or clipping (paring off) of the rim of the coin. However, it does not detect sweating, or shaking coins in a bag and collecting the resulting dust. Since this technique removes a smaller amount, it is primarily used on the most valuable coins, such as gold.
In early paper money in Colonial North America, one creative means of deterring counterfeiters was to print the impression of a leaf in the bill. Since the patterns found in a leaf were unique and complex, they were nearly impossible to reproduce.

In the late twentieth century advances in computer and photocopy technology made it possible for people without sophisticated training to easily copy currency. In response, national engraving bureaus began to include new more sophisticated anti-counterfeiting systems such as holograms, multi-colored bills, embedded devices such as strips, microprinting and inks whose colors changed depending on the angle of the light, and the use of design features such as the "EURion constellation" which disables modern photocopiers. Software programs such as Adobe Photoshop have been modified by their manufacturers to obstruct manipulation of scanned images of banknotes.