The leading X-ray computed microtomographic imaging facilities can now provide 10243 voxel images of rock and other porous media samples at a voxel resolution of under 5 microns. Such data sets are extremely rich in information, and overwhelming in size; a 10243 data set corresponds to a gigabyte of character data. Automated computer analysis is necessary in order to extract quantitative information from such images. In this paper we discuss automated extraction of geometrical features using computerized image analysis. Typical algorithms required include segmentation to identify the material type of each voxel in the image; medial axis reduction of objects in the image to provide a skeleton enabling efficient searching and geometrical characterization as well as a network for the application of graph theoretic tools; feature extraction; measurement of length, cross sectional area and volume; and stochastic characterization of measured properties. With current memory limitations in desktop workstations, data sets beyond 5123 voxels in size require parallelization of the algorithms.