Many security documents, such as share certificates, cheques and identity documents (e.g. passports), are initially preprinted in skeletal form without individual identifying (variable) data and then later on, when used, the appropriate variable data is printed thereon using a laser printer. Typically, the generation of the variable data, and control of the printer, is by means of a computer.
However, the current widespread usage of laser printing, to apply variable data to security documents, has increased the need for means to protect such data against fraudulent alteration since the toner image used to create a laser-printed image may be fairly readily removed from the document by scraping or dissolving it away. If this is done, substituted (false) data may then be applied to the document to alter the variable data thereon.
One approach for eliminating the foregoing risk of data alteration which is associated with laser-printed documents is to protect the toner image against removal. Many such protective devices have been developed in the market-place, for example, one which applies a laminate patch of transparent material over the area of the document containing the data so that any attempt to alter the data (toner image) would necessarily change the overall appearance of the document.
A second approach for deterring any fraudulent alteration of laser-printed variable data, over that referred to above, has been developed by the inventors herein. Specifically, the inventors have conceived and developed an alternative approach which protects against such alteration by configuring the variable data in such a manner as to enable ready visual detection of any substitute data appearing on a document in place of original variable data. Thus, this means of protection is not intended to physically prevent the removal of a toner image comprising variable data but rather, is directed to enabling one to readily detect if and when any such removal has taken place. If such is detected it may then be concluded that the document comprising the altered data is not authentic and invalid.