[re9]

Scanning printed material probably, newspaper photos are made of dots... Printing + scanning artifact -- https://www.scantips.com/basics06.html https://photo.stackexchange.com/questions/70139/what-caused-...

[rbanffy]

Also, how to fix it: https://www.getrevue.co/profile/shift-happens/issues/moire-n...

[re9]

Probably easier with ImageMagick: https://legacy.imagemagick.org/Usage/fourier/#noise_removal