lighting is everything, - i've had skin with practically no detail look very realistic because of proper lighting. - heck even real life pictures can look bad with the wrong lighting lol - spend a little more time getting to know the Visual panel options and familiarizing yourself with how each different light ( bulb ) affects the image - learn to use different IBL ( image based lighting ) settings and images - the default lighting settings are not very good so even if you used realistic skins, it will look cartoon ish. Pay extra attention to how the shadows fall on your character and controlling the highlights. the Realistic look is not just an obvious color, but subtle subconscious things like the angles of the shadows falling correctly - like when you look at an image ..and feel something is not right ...vs the obvious - subtle things like how the shadows look under the neck vs the way the background is supposed to light the scene.
Also, I've discovered that realistic lighting tends to have both a blue and a yellow hue - more blue for cold weather ...more yellow for warm weather. Spend more time looking for the perfect lighting set up than the perfect skin. The proper light set up can make a plain image with no detail look realistic - I created this character from a mask photo - no realistic details at all, yet the lighting gave it new life. also notice the subtle nuance of how the image background shadows fall in line with how the shadows on the character fall. Every little detail that's off ...distracts from realism.
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"To define Tao is to defile it" - Lao Tzu