If you are a member, you can access a collection of royalty-free reference photos that can be used to create artwork. These are all photos I have taken myself and I add new photos often. Here is a free sample of a few images: https://shwca.se/free-ref
There is also a gallery of images submitted by members. This located on my Discord server.
Not yet a member?Join for as little as $5/month, plus get access to other benefits like slower versions of my YouTube tutorials: https://www.patreon.com/join/aaronrutten