This disclosure describes an efficient architecture for an imaging device that supports image registration for still images and video coding of a video sequence. For image registration, the described architecture uses block-based comparisons of image blocks of a captured image relative to blocks of another reference image to support image registration on a block-by-block basis. For video coding, the described architecture uses block-based comparisons, e.g., to support for motion estimation and motion compensation. According to this disclosure, a common block comparison engine is used on a shared basis for both block-based image registration and block-based video coding. In this way, a hardware unit designed for block-based comparisons may be implemented so as to work in both the image registration process for still images and the video coding process for coding a video sequence.