I was hunting this for quite a while. This particular coin only affects Denmark 1812 12 skilling which is overstruck over 1771 1 skilling.
You can see the number "1771" right above the King's head. I unfortunately do not have a 1771 1 skilling photo to compare with - google images do have some examples.
As of why 1771 1 skilling was chosen, I have no idea. Perhaps this was the only copper coin available? Many coins prior to this were struck in cheap silver billion. Also do note - this coin seems to be cut down / shaved from the original coin! Perhaps when it was overstruck, it became enlarged and had to cut down to shape. This does have an interesting edge as well.
Would be interested to know more about this history!
More world overstruck coins can be seen here: