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As mentioned several times in this blog, it is always better to draw from life. Photographs inherently have numerous distortions in contour, tone value and perspective. Of course working from live models is not cost effective for many of us.
A sculptor will draw differently than a painter because his interests are in form rather than color. A contoured line defines form, so a linear drawing will be more useful. Sometimes I draw directly on a xeroxed copy of a photo to help better understand this form.
In a preparatory drawing for a painting one generally needs to mass-in tonal areas separating the dark from the lights.
In some areas of these drawings, I have created tonal shapes next to light areas that define a particular plane, as well.