Changeable Laser Image (CLI)
A changeable laser image is two or more pictures engraved into the same area of a polycarbonate document beneath a lenticular lens structure, so that tilting the card swaps which one you see. One angle shows the holder’s portrait; another shows their date of birth or document number in the identical patch of surface.
| Abbreviation | CLI |
| Mechanism | Interleaved images laser-engraved under a lenticular lens array |
| Tilt direction | Side to side, using vertical lens elements |
| Typical content | Portrait and document number, or portrait and date of birth |
| Requires | Polycarbonate, or another laser-engravable layered substrate |
| Close relative | MLI — multiple laser image |
| Also called | Tilt image, lenticular laser image |
How two images share one surface
The lens structure does the work. A row of narrow cylindrical lenses is formed into the card surface, and beneath them the two images are cut into fine interleaved strips — a slice of image A, a slice of image B, alternating.
Each lens only lets you see the strip directly beneath it at your current viewing angle. Look from the left and every lens shows you an image-A strip, which your eye assembles into the complete first picture. Move to the right and the same lenses reveal the image-B strips, and the second picture assembles instead.
Nothing moves and nothing changes. Both images are permanently present; the lens array simply controls which set of strips reaches your eye.
The engraving itself is not printed on the surface but carbonized inside the polycarbonate, which is why the feature is only practical on fused monolithic documents. There is nothing to lift and nothing to alter without destroying the lens structure above it.
Why CLI matters for identity verification
The security value is that it binds two pieces of data together physically. The portrait and the document number are not merely printed near each other — they occupy the same area of the same card, interleaved at strip level beneath a shared lens array.
Photo substitution has to defeat both simultaneously, in a material where any intervention destroys the lens geometry. That is a substantially harder attack than lifting a laminate.
For a verification flow the feature is angle-dependent, so it needs motion. A single photograph captures one of the two images and gives no indication that a second exists. Frames captured across a tilt show the switch, and the switch is what confirms the feature is real rather than a printed picture of one image. It sits with holograms and optically variable ink in the group of features that reward guided capture in identity document verification.
CLI vs MLI
| CLI | MLI | |
|---|---|---|
| Stands for | Changeable laser image | Multiple laser image |
| Tilt direction | Side to side | Top to bottom |
| Lens orientation | Vertical elements | Horizontal elements |
| Typical images | Two, switching between them | Two or more in sequence |
| Underlying technique | Laser engraving under lenticular lenses | The same |
The two are frequently treated as interchangeable, and the technology underneath is the same. The practical difference is the axis: a CLI switches as you tilt the card left and right, an MLI as you tilt it up and down.
What a CLI can’t do
A still image misses it entirely. One frame shows one image and no evidence that another exists. Without motion the feature contributes nothing.
Viewing angle has to be right. Between the two positions is a transition zone where both images are partly visible and neither is legible. A capture caught mid-switch is unusable.
It is substrate-dependent. The feature needs a laser-engravable layered material, so it appears on polycarbonate and not on laminated paper or PVC cards.
It binds data, not identity. A CLI proves the portrait and the number were personalized together on genuine stock. Whether the person presenting the card is its owner is a separate question, answered by liveness detection.
Frequently asked questions
What is the difference between CLI and MLI?
Mainly the tilt axis. A changeable laser image switches as the document is tilted side to side, using vertical lens elements; a multiple laser image switches top to bottom, using horizontal ones. The underlying laser-engraving and lenticular technique is the same.
Why can’t you see both images at once?
The lens array only lets you see the engraved strips directly beneath each lens at your current angle. Both images are permanently present as interleaved strips; the lenses control which set reaches your eye.
Can a CLI be faked?
Not easily on a genuine-looking substrate. It requires laser engraving inside layered polycarbonate under a formed lens structure. A printed imitation shows one fixed image and does not switch.
Do driver licenses have CLIs?
Some do, particularly polycarbonate national ID cards and licenses in Europe. It is uncommon on laminated PVC cards, which cannot support the engraving or the lens structure.
