A fundamental task during underground excavations is to establish a model for understanding the rock mass behavior. Continuous data acquisition during excavation work updates such model whereas rock mass characterization in terms of the geometry of a rock mass and its discontinuities contributes importantly. By using digital photos and computer vision this task is strongly supported. Some general impacts are increased safety, faster data acquisition at higher quality, and permanent objective records that allow later reviews. Particular advantages of the computer vision approach are (i) data acquisition in less than 5 minutes, (ii) no external surveying, (iii) no bulky equipment, and (iv) no special expert knowledge is required.