Photochromic Ink is a colored or colorless ink that when exposed to UV or sunlight, instantly change color. Once the source of the UV light is removed, the ink will change back to its original color.
This Photochromic Ink feature is effective primarily in document-present situations where the original document can be examined by a trained professional or scanned with a specialized 3-illumination ID scanner and analyzed with adequate forgery detection technology.
Usability in online and mobile onboarding situations is challenging as the examination is made not on the physical document but on a photograph or scanned image of it.
Ref.: https://www.perfectcloud.io/resources/glossary