How much human anatomy do you need to specify? Do you need to put hands, feet, legs, eyes, mouth? Or should you only tag things that are prominent in the image?

tagging eye color (ex. blue_eyes vs brown_eyes) has value because it describes something that can be used to distinguish between different characters/images

tagging eyes does not have value because everyone is assumed to have eyes by default. it is instead more valuable to tag some trait about the eyes, for example if a character has a non-standard number of eyes it's useful to tag one_eye, three_eyes, multiple_eyes etc.

same for other things.
thighs is not useful. thick_thighs is.
mouth is not useful. open_mouth is.
feet is not useful (even though it's used a lot). foot_focus is.

if it has no value as a search term, it shouldn't be tagged.