Shhh... Can I Tell You a Secret?
Illustrators usually work from photographic reference.
Not Only That...
They use things like opaque projectors and light boxes from time to time, too, and... well... trace.
I Know This Because I Was One
For 20 plus years I was a freelance illustrator.
Nearly 100 of my paintings have been published as book covers for clients like HarperCollins, Simon & Schuster, Macmillan and Scholastic.
Countless paintings have also been published as illustrations for magazines, advertising, children's books and textbooks.
In the latter years of my illustration career I pioneered the use of digital painting methods, too.
In fact, my digital paintings were featured in five consecutive editions of The Painter Wow! book by Cher Pendarvis.