Background: The use of photographs to diagnose and monitor skin diseases is gaining ground. Objectives: To investigate the validity and reliability of photographic assessments of atopic dermatitis (AD) severity. Methods: AD severity was evaluated in the clinic by two assessors using the Eczema Area and Severity Index (EASI), SCOring Atopic Dermatitis (SCORAD), and Investigator's Global Assessment (IGA). Participants photographed the lesions with their own smartphone and completed a questionnaire about the extent of eczema the same day from home. The photographs were assessed twice with an 8 weeks interval by five dermatologists experienced in photographic evaluations. Intraclass correlation coefficients (ICC) with 95% confidence interval (CI) were applied. Results: Seventy-nine participants were enrolled. The ICC between clinical EASI and photographic EASI was 0.88 (95% CI 0.81–0.93), and 0.86 (0.70–0.93) between clinical SCORAD and photographic SCORAD. Perfect agreement between clinical IGA and photograph IGA was observed for 62%, with the difference between the two never deviating with more than 1 score. The inter-rater ICC for photographic EASI and photographic SCORAD, respectively, was 0.90 (0.85–0.94), and 0.96 (0.91–0.98). The intra-rater agreements between the first and second assessments varied from 0.95 to 0.98 for photographic EASI, and from 0.86 to 0.94 for photographic SCORAD. Conclusion: There was high agreement between mild to moderate AD severity assessed clinically and based on smartphone photographs. Further, the photographic assessments can be reproduced with high reliability.