1. A non-invasive method for characterizing keratinocytes, comprising: comparing, by one or more computing device, an unknown image segment to a known keratinocyte model image segment to determine the degree of match between the unknown segment and a model of a keratinocyte; comparing, by the one or more computing device, the determined degree of match to a predetermined value; and characterizing, by the one or more computing device, the particular segment of the sample as a keratinocyte based on the determined degree of match; wherein the degree of match is identified by determining a difference value between reflectance gray-values of the particular segment of the diagnostic image and a value derived from the model of the keratinocyte; wherein characterizing the particular segment of the sample as a keratinocyte comprises characterizing the particular segment of the sample as a keratinocyte if the determined difference value is equal to or below a predetermined threshold; and wherein the predetermined threshold is from 0.4 to 0.6.