I think image cropping should also include cropping of certain body parts that are sexualized or used as fetish.
Just because someone enjoy feet or armpits it shouldnt be left rule free just like cropping focused on breast or ass.
The cropping is intentional to focus on said kinks and not because the art is good or not.
If the intention was posting a good art that has a nice looking feet/armpit/other parts the person would just post the whole image instead of cropping said parts.
As 4 on NSFW rule state "No asset cropping. Cropping otherwise appropriate images to focus specifically on genitalia or to make it seem sexually suggestive is generally forbidden."
So i think that armpit and feet should be added to this, like i said before if the intention was sharing a good art, why crop it?