I do apologies but I refuse to put the mature tag because I simply don't think female's nipples are vulgar.
Especially in this context.. I see no difference between males and females nipples..
Don't report it, don't sexualize this anatomy study.
if you are interested on patreon you can find more "normal"reference sheets for $1 per month!
use it for your exercises if you need, but don't trace it please X'D
If you want to show me the result, do it here or on my facebook page! I'll appreciate it XD