I don't know what this is called or if it's a thing but I was playing around and I think it looks cool (enough to share).

1. Take an image of a coin, make a copy of it.
2. Scale the copy by some huge number so that the pixels are huge and visible, (using interpolation None).
3. Put the scaled copy underneath original.
4. Set original opacity to be about 60%.
5. Merge Down, then play with brightness and contrast and or hue/saturation.

Because numismatist and numismatics are genitive of numisma, I would call it Numisma art or Numism art?

wow, what a weird word to remember I'll probably forget to use it but if someone mentions it it might click.

What is specific to coins? You can do this with any image?

I guess yeah, it's just when I played with it I was using coin image.

just pretend that numisma is from latin numerus (number) because they have the same prefix (which is wrong but can help to remember... )

Now the real definition from > https://www.merriam-webster.com/dictionary/numismatic
I quote:
The noun numismatics and the adjective numismatic came to English (via French numismatique) from Latin and Greek nomisma, meaning "coin." Nomisma in turn derives from the Greek verb nomizein ("to use") and ultimately from the noun nomos ("custom" or "law").