8:00 PM, Thursday September 30th 2021
You should definitely continue to rely on your reference image throughout the whole process. That doesn't mean that you're copying it directly, but rather that you should still be referring to it to help inform you of the nature of the textural forms that are present there. From there, you can use that information to choose how to design your shadow shapes to imply the presence of those forms, but you won't be bound strictly to drawing the shadow shapes you actually see in your photo ref.