Another fun one is the "EURion constellation", a set of features on printed currency that photoshop and color copiers will read and then refuse to operate on: h

Another fun one is the "EURion constellation", a set of features on printed currency that photoshop and color copiers will read and then refuse to operate on: https://en.wikipedia.org/wiki/EURion_constellation https://en.wikipedia.org/wiki/EURion_constellation