Infrared thermography (IRT) can be used in remote recognition of potential weakening features of a rock cliff like shallow holes, high fracturing, moisture or material inhomogeneities, providing useful information for the corresponding rock mass geo-engineering characterization. A method aimed at such a recognition is proposed here together with its MATLAB implementation (IRTROCK package). It is based on the acquisition of a series of IRT images during the night-time cooling of a rock mass and on the search for possible anomalous thermal transients. The IRT alone is unable to completely characterize a rock mass; a meaningful interpretation of the results requires a geological on-contact survey or other on-contact or contactless techniques. Nevertheless, the results obtained in a portion of the cliff, where a detailed study with other techniques has been carried out, can be advantageously extended to the whole cliff. Moreover, the IRT measurements can be easily and safety repeated over time to evaluate possible changes that affect the studied rock mass. The effectiveness of the proposed approach has been verified in two test sites.