Lighting
High-key: bright light, use of filler lights, few shadows, magazine covers often use it to highlight cover model.
Low-key: fewer filler lights to create shadows and contrast between light and dark, a thriller might use this to create a sense of mystery.
Artificial: use of electric lighting, often in an outdoor setting or studio.
Natural light: use of daylight, can be used symbolically: bright light associated with good, dark connotes evil.