Since men and women first learnt to use charcoal and stones to make marks on rocks in caves they have been obsessed with capturing what they see around them.
"Study for the Libyan Sibyl" by Michelangelo
The human form in all its odd, beautiful, exotic, strangeness has been for many artists their Achilles heel. Without references to guide our hand, to delight the eye and inspire the imagination - artwork would remain as cave paintings warning people not to enter in case of bears.
"Vitruve Luc Viatour" by Da Vinci
Leonardo Da Vinci
Each artist depicts what they see in their own unique way. Some try to emulate and some forge their own path, but no matter how you are inspired or what media you use to create your work - remember the lessons of other painters who came before.
"Dance Class" by Edgar Degas
Look, and see with your own eyes at the world around you. Use references of structure, light, depth to make your own work more realistic.
"Portrait of Daniel Henry Kahnweiler" by Pablo Piccaso
With the development of the internet, artists no longer even need to leave their studios to be exposed to a veritable wealth of digital stock sources and references on any subject they can possibly imagine. However, every digital image is flawed in that it is a 2D representation of a 3D subject. You can not turn a photo to see how shadows change on the face of a child, you can not move a models arms into a better pose and you are subject to the creators vision as they took the image or created it digitally.
"This is Not a Pipe" by René Magritte
Recognizing and understanding this limitation of digital stock and reference images or indeed even a 2D pencil sketch drawn whilst a subject was sat in front of the artist - should help you to compare more subjectively the differences between a flat 2D image and a 3D subject. This flaw reinforces the need to "see" with your own eyes, to touch and experience shadow and light on a subject, enabling you ultimately to create a better representation of what you envision in your artwork.