Techniques and tools for high dynamic range (“HDR”) image generation and rendering are described herein. In several described embodiments, images having distinct exposure levels are aligned. In particular embodiments, the alignment of a reference image to a non-reference image is based at least in part on motion vectors that are determined using covariance computations. Furthermore, in certain embodiments, saturated areas, underexposed areas, and / or moving objects are ignored or substantially ignored during the image alignment process. Moreover, in certain embodiments, a hierarchical pyramid block-based scheme is used to perform local motion estimation between the reference image and the non-reference image.