The paper presents results the aim of which was to examine the possibility of applying the methods of image analysis and mathematical morphology to petrography and rock mechanics. These methods have not found so far greater application to the microscopic analysis of rocks, chiefly due to the variety of rock structures. On the other hand, their application may enable considerable improvement of the conducted geometrical measurements of rock structures. The study discusses the results obtained due to the operation of algorithms of automatic analysis for 3 rocks: granite (from Strzelin), dolomite (from Redziny) and sandstone (from Lipka and Radlin). In order to evaluate the correctness of the automatic methods, the obtained results have been compared with the results obtained in a standard (non-automatic) analysis. The obtained results allow to state that in the case of the examined rocks the author has proposed fairly correct method of image analysis of rock structures based on the image analysis and mathematical morphology transformations.