Research on plant leaf diseases requires the acquisition of quantitative data to characterize the symptoms caused by different pathogens. These symptoms are frequently lesions that are differentiated from the leaf blade by their color and texture. Among the variables used to characterize the impact of a disease, the most relevant are the number of lesions per unit of leaf area, the area and the shape of the lesions. Since visual measurements are only possible on small numbers of images, it is necessary to use computerized image analysis procedures. The LeAFtool (Lesion Area Finding tool)