Artist Cali Rezo's portraits are not digitally-manipulated photographs but rather tablet/pen illustrations drawn from reference photos. Amazing. From the "How do I work" section of her mostly-French language site:
I work with a tablet and a pen directly on the computer. Besides, my crafting is quiet "traditionnal":Link (via Drawn!)
I use photographics references (I shoot everything that moves... and everything that does not also, haha !). I start with a sketch (with my electronic pen, huh, not on paper, no, no, no !)( and I don't draw ON the photo). Then I paint the light and dark flat tints. And I tune the color tints and the finess of the strokes.