Security Printing
Security printing is the field of the printing industry which deals with the printing of items such banknotes, passports, tamper-proof labels, product authentication, stock certificates, postage stamps and identity cards. The main goal of security printing is to prevent forgery, tampering or counterfeiting

A watermark is a recognizable image or pattern in the paper that appears lighter or darker than surrounding paper when viewed with a light from behind the paper, due to paper density variations. A watermark is made by impressing a water coated metal stamp or dandy roll onto the paper during manufacturing. Papermakers use watermarks also to identify their products.

Intaglio is a printing technique in which the image is incised onto a surface. Normally, copper or zinc plates are used, and the incisions are created by etching or engraving the image, but one may also use mezzotint. In printing, the surface is covered in ink, and then rubbed vigorously with tarlatan cloth or newspaper to remove the ink from the surface, leaving it in the incisions. A damp piece of paper is placed on top, and the plate and paper are run through a printing press that, through pressure, transfers the ink to the paper.
The very sharp printing obtained from the intaglio process is hard to imitate by other means. Intaglio also allows for the creation of latent images, which are only visible when the document is viewed at a very shallow angle.

Geometric Late Work
A guilloche is an ornamental pattern formed of two or more curved bands that interlace to repeat a circular design. They are made with geometric lathe.

This involves the use of extremely small text, and is most often used on currency and bank checks. The text is generally small enough to be indiscernible to the naked eye. Cheques, for example, use microprint as the signature line.

Optically Variable Color Changing Inks
Colour changing inks are inks containing pearlescent pigments that change colour when viewed at a different angle. The colour of the ink does not actually change, but the angle of the light to the viewer's eye changes and thus creates the change in colour. A number of types are available, including green to purple, gold to green and green to lilac.

A hologram may be embedded either via hot-stamping foil, wherein an extremely thin layer of only a few microns of depth is bonded into the paper or a plastic substrate by means of a hot-melt adhesive (called a size coat) and heat from a metal die, or it may be directly embossed as holographic paper, or onto the laminate of a card itself.

Security Threads
There are two kinds of security threads. One is a thin aluminium coated and partly de-metalized polyester film thread with micro printing, which is embedded in the security paper as banknote or passport paper. The other kind of security thread is the single or multicolour sewing thread made from cotton or synthetic fibbers, mostly UV fluorescent, for the bookbinding of passport booklets.

Magnetic INC
Because of the speed with which they can be read by computer systems, magnetic ink character recognition is mostly used in banking, primarily for personal checks. The ink used in Magnetic Ink Character Recognition (MICR) technology is also used to greatly reduce errors in automated (or computerized) reading.

Serial Numbers
Serial numbers are not difficult to forge, but make legitimate documents easier to track and audit.

Anti-Copyng Marks
In the late twentieth century advances in computer and photocopy technology made it possible for people without sophisticated training to easily copy currency. In an attempt to prevent this, security printers have sought to add filtering features to the software and hardware available to the public that senses features of security documents, and then locks out the reproduction of any material with these marks. One known example of such a system is the EURION constellation.

Copy-Evident Paper
Many secure documents have the feature, which causes a photocopy of the document to appear obviously different from the original. For example, when photocopied, most checks will display the word "VOID" (or the equivalent in another language) on the copy, even though it is absent from the original.

Fluorecent Dyes
Fluorescent dyes are dyes, whichfluoresce under ultraviolet light or other unusual lighting. These show up as words, patterns or pictures and may be visible or invisible under normal lighting. This feature is also incorporated into many banknotes and other security documents. Some producers include multi-frequency fluorescence, such that different elements fluoresce under specific frequencies of light.

Electronic Devices
With the advent of RFID (Radio-frequency Identification), it is possible to insert extremely small RF-active devices into the printed product to enhance document security.

Thermochromatic Ink
Security ink with a normal "trigger" temperature of 88 degrees F, which will either disappear or change colours when the ink is rubbed.

Latent Images
Pressure sensitive or hot stamped labels characterized with a normal (grey or coloured) appearance. When viewed via a special filter (such as a polarizer) an additional, normally latent, image appears.