05 Jul 20227 min readin Forensics & authentication

How Optical Illusions Help Secure Identity Documents

Arif A. Mamedov

President and CEO at Regula Americas, Ph.D.

What do good old souvenir stereo cards with a girl winking her eye and identity documents have in common? It could be the girl of course (at least her non-winking version), but what we’re actually talking about is the technology, namely lenticular printing.

Don’t be fooled by the playfulness of those stereo advertising or the whimsy of scenes on souvenir cards – lenticular technology is a proven method to secure such sensitive documents as passports, driver’s licenses, vehicle registration certificates, and so on. We at Regula have been meticulously studying various types of identity and security documents for years, and we know for sure what to pay attention to when verifying a document. 

The idea of optically variable images goes back in centuries. It all started with wooden tabula scalata and double portraits by known and unknown artists, like the 18th-century work of French painter Gaspar Antoine de Bois-Clair depicting King Frederik IV and Queen Louise of Mecklenburg-Güstrow of Denmark.

Gaspar Antoine de Bois-Clair, Double Portrait of King Frederik IV and Queen Louise of Mecklenburg-Güstrow of Denmark

Gaspar Antoine de Bois-Clair, Double Portrait of King Frederik IV and Queen Louise of Mecklenburg-Güstrow of Denmark, ca. 1700. The collection of M.S. Rau gallery, New Orleans. Source of the image: artsy.net

However, lenticular printing in its modern application, which supposes using lenticular lenses, appeared much later. There were a number of experiments on optical illusions with images throughout the 19th century, but the sheets with lenticular lenses that made pictures “move” depending on the angle of view came to life closer to the 1930s. The advancement of this technology resulted in a burst of stereo advertising in the 1960s.

dancing girl lenticular print

Source of the image: gifer.com

Starting with the last decade of the 20th century, lenticular printing widely became a security element in identity documents that were made of plastic or contained polymer pages. It’s rather hard and expensive to forge a document with a lenticular image, as lenticular lenses are embossed onto a polymer substrate that forms an identity card or a special polymer page in a paper document. Such security elements are present, for example, in Estonian, Finnish, Austrian, French, or US IDs, as well as in other national identity documents.       

So, what exactly is lenticular printing? The term “lenticular” is used for repeating rows of convex lenses on the front surface of a plastic sheet. At the same time, the reverse side of this sheet is totally flat. Each lens magnifies and projects micro-slices of images (usually two, but can be more) printed on the reverse side of lenses or directly on paper.

Lenticular technology scheme

Lenticular technology scheme

Lenticular technology means that initial images are cut into stripes and then interlaced with each other so that there is a pair of stripes under each lens – one stripe from one image and the other stripe from the other image.

lenticular printing in Estonian IDs
lenticular printing in Estonian IDs 2
lenticular printing in Estonian IDs 3

Scheme of forming an image for lenticular printing. Identity card of Estonia, 2011

Each lenticular lens magnifies and isolates only one of the initial images. That’s why an observer needs to move a card or a page either side-by-side or top-to-bottom to see all the printed images.

Image when viewed at different angles

Image visualization when viewed at different angles

For the sake of advertising or amusement lenticular technology makes a depicted person, for example, wink or gulp a soft drink. There can be even a short animation, especially if there are more than two images coded in the printing. But what about passports or identity cards? Hardly we’ll see a winking holder of a document. Usually, lenticular images in IDs show national symbols, and personal information, such as date of birth, the number of a document, a photo of a holder, etc. Depending on what data is printed with lenticular technology, there can be two possible methods of printing.

The first one is referred to as a multiple laser image (MLI) or changeable laser image (CLI). This means that the initial images are applied by laser engraving under lenticular lenses. For identity documents, this option usually presupposes that a lenticular field is empty and is filled with personal data by the laser when personalizing the document. This was MLI/CLI that was used for securing IDs with lenticular technology at its early stages – it was yet another way to encode personal data.

Passport of the Kingdom of Saudi Arabia sample
lenticular printing in a passport of the Kingdom of Saudi Arabia

Passport of the Kingdom of Saudi Arabia, 2020

Later on, as the application of lenticular printing in identity documents evolved, another method of printing started to gain popularity – the so-called Dynaprint®. This method derives from the classic lenticular technology, when cut into stripes images are printed under lenticular lenses on a flat surface. It is used for standard lenticular fields that are common for a certain type of document, they usually contain some national symbols, emblems, flags, and so on, but no personal data. This peculiarity is easily explained: lenticular lenses with everything printed under them are embossed into the polymer substrate that forms an ID, so it’s impossible to foresee which personal data this exact document might contain.

Passport of the Republic of Latvia, 2015 sample
lenticular printing in a Latvian passport

Passport of the Republic of Latvia, 2015

Naturally, an identity document can employ both lenticular printing methods.

Identity card of the Republic of Austria, 2021 sample
lenticular portrait
lenticular printing in Austran passport

Identity card of the Republic of Austria, 2021

Lenticular technology undoubtedly contributes to the security of identity documents, making it harder for law violators to forge an ID. Unlike special luminescence, this security element is verified with the naked eye. However, without special reference systems, comprehensive databases, and profound knowledge it’s not that easy to tell a forged document from an authentic one judging just by the presence or absence of lenticular images. There isn’t one person who knows all the security elements and features of all IDs in the world. Moreover, identity documents are constantly changing to make fraud almost impossible. In such a situation, information is the key to success. If an officer or an ID verification system can refer to a reliable database of identity documents, their examination of any document will be more comprehensive. 

Thirty years of Regula’s intense investments in forensics resulted in the world’s largest document templates database that contains over 11,000 templates for IDs from 248 countries and territories. And it never stops growing as new identity documents are released all over the world. Moreover, this profound knowledge has become the foundation for the impeccable performance of the company’s forensics devices and identity verification solutions. The hardware is designed and tuned to point out the most important features that create the difference between a legitimate document and a forged one. And Regula software relies on this document templates database to enable the most comprehensive ID verification both in a forensic lab or at a border authority counter, as well as on web and mobile platforms. 

To learn more about various security elements in identity documents, please check Regula’s extensive glossary, which describes them all.

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