1. An image classification method in a digital image processing system for automatically classifying a plurality of captured digital images, the method comprising using a digital image processor to perform the steps of: receiving a plurality of digital images to be classified, each digital image having associated geographic image capture metadata; determining a first grouping value according to the associated geographic image capture metadata for each of the plurality of digital images to be classified; defining the first grouping value for each digital image as a distance between the geographic image capture metadata for each digital image and a relative geographic reference point; calculating an average of said determined first grouping values; computing a variance metric of said first grouping values, relative to said average; determining from said variance metric a first grouping threshold applicable to said first grouping values; identifying first grouping values beyond said first grouping threshold as group boundaries; assigning said digital images to a plurality of digital image groups based upon said group boundaries; determining a second grouping value for each of the plurality of digital images to be classified; calculating as to one or more of said digital image groups, a group average of said second-grouping values of respective said digital images; computing a variance metric of respective said second-grouping values relative to each said average; determining from each said variance metric a respective second-grouping threshold applicable to the respective said digital image group; identifying ones of said second-grouping values beyond respective said second-grouping thresholds as subgroup boundaries of respective said digital image groups; and assigning said digital images of each of said one or more digital image groups to a plurality of subgroups based upon respective said subgroup boundaries.