Visual Cryptography
Visual cryptography, introduced by Naor and Shamir, splits a secret image into multiple apparently random shares that the human visual system decrypts by simply stacking them — no computation needed.
Purpose
It decrypts images without computation, requiring only the physical stacking of shares, fitting physical access control and watermarking.
Mechanism
Each pixel is split into n sub-pixel patterns distributed across n shares; in any single share the sub-pixel patterns appear with equal probability (looking random), but when stacked, white pixels stay white while black pixels show black, restoring the image visually.
Use cases
- Physical access control
- Image watermarking
- Computation-free decryption scenarios