For a long time the conservation state of works of art has been made qualitatively by experts, in general resulting in subjective results. A fast, practical and semi·quantitative method to perform this study is to use image analysis, whereby the image is subdivided into areas characterized by the same degree of alteration, determined in a semi-manual way by a restorer and analyzed automatically by software. This methodology has been applied to a painting from Puebla that represents the Immaculate Conception, painted on basalt and using a unique technique. The results provide a semi-quantitative framework of the conservation stale of the work of art and show the areas most affected by weathering and aging processes. The method can be a useful tool for studying the degree of conservation of paintings on different support bases.