This picture was sketched from life, as were two posted earlier, Labrador and Dachshund Drawing. Very Small Dog and Pale-eyed Puppy were worked from my own photos.
There is a huge difference between drawings taken directly from life and those from photographs. Sketching from a photograph is by far the simpler process (objects do not move, the angles are predetermined) and there is information the artist will never discover by any other means - no one knew the exact positions of a horse's legs at the gallop or the air-foil movement of birds' wing feathers until the invention of the camera.
But the artist's eye looking at reality and looking at a secondary image will perceive totally different priorities. Somehow a leveling occurs with the photograph; not only is every detail visible but every detail is equal. Viewing the photographic image, the artist finds the corner of a man's collar as intriguing for pencil or brush to reproduce as the corner of his eye.
When you are looking directly at a living thing this lack of proper priority is far less likely to occur. What was emotionally important when you viewed your subject will, if you are careful, retain its importance in the finished work. Indeed, you may be forced to simplify to just those important elements in order to finish your study before your sitter moves too drastically!
It is this emphasis on the most expressive elements that gives a sketch from life its true liveliness. Drawing from life is twice the challenge of working from photography - it often results in twice the Art.