Stock photography is the supply of photographs, which are often licensed for specific uses. Conventional stock agencies charge from several hundred to several thousand dollars per image, while stock photography websites may sell for around USD 25 cents. Professional stock photographers traditionally place their images with one or more stock agencies on a contractual basis, while stock agencies may accept the high-quality photos of amateur photographers through online submission. Some online photo websites have created unique software to search for fitting stock photos, for example searching for complicated keyword combinations, color, shapes, and moods. Other search engines may seek to quantify the best photos by looking for elements as diverse as “bright lights,” “evidence of emotional connections between people,” and the tilt of faces.