1. A face detection method, comprising: (a) acquiring a digital image; (b) extracting a sub-window from said image; (c) applying separate sets of two or more shortened face detection classifier cascades, trained to be selectively sensitive to a characteristic of a face region, and another set of face detection classifier cascades insensitive to said characteristic; (d) identifying the face data as corresponding to a projection of said face within the digital image on one or a combination of the characteristic-sensitive classifier cascades plus a constant vector representing said face according to one or a combination of the characteristic-insensitive classifier cascades, thereby decomposing the face data into orthogonal subspaces for characteristic-sensitive and characteristic-insensitive conditions; (e) based on the applying and identifying, determining a probability that a face with a certain form of the characteristic is present within the sub-window; (f) based on the determining, applying an extended face detection classifier cascade trained for sensitivity to said form of said characteristic; (g) providing a final determination that a face exists within the image sub-window; and (h) repeating steps (b)-(f) one or more times for one or more further sub-windows from the image or one or more further characteristics, or both.