Classic drawing book by Andrew Loomis now in the Public Domain. There are bits an pieces here we can build upon, and learn as a community. en.wikipedia.org/wiki/Andrew_Loomis archive.org/details/andrew-loomis-drawing-the-head-hands
This is a completely free image Andrew Loomis Drawing the Head and Hands (potrace) 131 that you can download, post, and use for any purpose.
Image License: CC0 No Rights Reserved
You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission, and at no cost. This image is completely free.