Materials with heterogeneous microstructures do not deform uniformly under stress (mechanical or environmental). A new deformation mapping technique (DMT), which compares digital images of microstructures of the same field of view before and after deformation occurs, is reported. Two digital images are required: a reference image, taken before deformation; and a deformed image, taken after deformation. The displacements of pixels required to match the deformed image to the reference image are computed, and these displacements are used to calculate the percent deformation in the two principal directions. Results are presented as either a deformation map, as a histogram, or as data files containing the displacements at the corner of each pixel. Comparison with exact solutions generated on a simulated microstructure shows that the accuracy of this technique is quite good.