Cutaneous leishmaniasis (CL) primarily affects people in remote settings with limited access to health services. mHealth tools offer an opportunity to overcome knowledge gaps about clinical response to treatment. We evaluated the validity of the Guaral+ST mobile application for the remote assessment of therapeutic response in patients with CL, through photographs of lesions captured with the app by community health volunteers. Patients with confirmed CL were followed at weeks 13 and 26 after completion of treatment to assess therapeutic response in two clinical settings in southwest Colombia. Direct evaluation of lesions performed by an experienced physician was considered the reference standard. Photographs of lesions taken by CHV or nurse assistants with the mobile app, were independently evaluated by three physicians to define clinical response. A summary measure of clinical outcome defined by the three physicians was considered the index test. Sensitivity, specificity, and positive and negative predictive values were estimated. Interrater reliability (kappa) was calculated. Among 53 participants with CL who had at least one follow-up visit, the sensitivity of therapeutic response evaluation through photographs taken with the Guaral+ST app, compared with direct evaluation by an expert physician, had high validity with sensitivity of 100% (95% confidence interval: 80.5–100%) and specificity of 97.2% (95% confidence interval: 85.5–99.9%). The chance-adjusted agreement (κ) was > 0.8, which is conventionally characterized as almost perfect. The high accuracy of the remote evaluation of photographs for the assessment of therapeutic response supports the use of mHealth tools for improving access to treatment follow-up for CL.