18. The digital image processing method as recited in claim 17 , wherein said sub-step of performing discretization uses constrained K-means clustering.
18. The digital image processing method as recited in claim 17 , wherein said sub-step of performing discretization uses constrained K-means clustering. 20. The digital image processing method as recited in claim 18 , wherein said at least one hard constraint includes a positive constraint based on predetermined knowledge that two persons found in different images from said plurality of digital images are the same person.