The Monkey Head Nebula also known as NGC 2174 is an emission nebula near the top of Orion’s raised arm. It’s slightly larger in the sky than the full moon and is about 6,400 light years away.
This was 17 hours of data and though it was relatively bright in both OIII and SII, the hydrogen alpha was soooooo much brighter that it overwhelmed the other signals. In this SHO image it would have made the image essentially green. To show some of the details of the other elements, I toned down the green part to let the oxygen and sulfur show through more easily.
In most catalogs, NGC 2174 refers to the nebula while NGC 2175 refers to an open cluster apparently contained within the nebula (it could be in front or behind).
For all the technical details see astrobin.