On the certified copy of a document (e.g. death certificate) is a watermark that won’t come through if you try to colour scan it, and it comes through much more faintly on a camera than it appears to the naked eye. How does this happen?
In: Technology
Special inks and dyes. Basically using a certain type of ink, you can create something that disappears under the intensely bright light used in photocopying or flash photography. It’s a similar concept to the clothing some celebrities wear that ruins photographs by paparazzi. [Example here](https://petapixel.com/2015/02/25/watch-flashback-anti-paparazzi-clothing-ruin-flash-photographs/).
In addition to dyes and inks, the actual physical printing can affect copying. Use of slightly angled embossing (raising the ink to not sit flush with the paper) can create a similar effect.
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