According to science, shadow is an image of an object created on a flat surface due to obstruction of light. In the eyes of art loving people, shadow is not just a 2D  impression or image of an object on a flat surface but much more than this. Shadows add emotions, feelings and depth to a scene. Marvelously captured shadows enhance the beauty of the photograph. Ruth E. Renkel expressed shadows beautifully:

Never fear shadows.
They simply mean there’s a light shining somewhere nearby.

Shadow of a building
Llanthony Priory at dusk, Flickr
Shadow of a badminton player
Flickr
Shadow of a parrot
Flickr
Russ-And-Reyn-Artwork
Russ and Reyn Artwork
Russ and Reyn Artwork, Newyork
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Russ and Reyn Artwork, Shadows and Photography
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Shadow Photograph Flickr
Flickr
Shadow of stairs
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Flickr

Flickr

Flickr

Shadow of a fork Flickr
Shadows of trees on a house
Flickr
Shadow of plants