In 1696 the famous mathematician and scholar Isaac Newton was employed by the English Mint (now the Bank of England) to bring order to the English currency. Three hundred years later the Bank of England is employing a consortium of English mathematicians to bring disorder and CHAOS to the English currency.

If you take an Australian $5 note, hold it between your fingers, with the Queen facing you, and then lift the note to the light, in the top left-hand corner you will see a very faint image of the Australian emblem. It is a watermark that has been embedded in the note during manufacture. In the past, it has been difficult to forge watermarks, and so they have provided some protection against counterfeiting. However, this is no longer true as criminals can use sophisticated scanning devices coupled with powerful computers to create forged notes. To counter this the Bank of England are considering partially 'hiding' the watermark with a random set of dots.

Minute microdots will be placed, apparently randomly, on top of the watermark, creating a mask to hide it. Sometimes, the mask is like a complex fractal and is generated through fractal modulation.
The counterfeiters may have no problem reproducing the watermark, but they will find it almost impossible to reproduce the mask. The mask has become the secret code. Moreover decrypting the code from the bank's point of view is as simple as scanning the note. The trick is partly due to high precision printing. When a note is scanned to produce a counterfeited copy, the image will be slightly blurred. Thus a bank scanning any note can do a statistical analysis of the masked watermark, to check if it is a counterfeit.