This validation study is designed to evaluate the sensitivity, specificity, validity and reliability of digital photography of the skin as a prevalence assessment tool in preparation for the National Health and Nutrition Examination Survey, 2001 (NHANES IV). NHANES is charged with monitoring disease in the U.S. population, which is affected frequently by skin disorders and disease. The three skin disorders proposed for study in NHANES IV are atypical nevi, psoriasis, and hand dermatitis. This selection is based on the expected impact of these diseases on the U.S. population, including a prevalence of 3-10%, associated risk of melanoma in the case of atypical nevi, and associated disability in the cases of psoriasis and hand dermatitis.