Tracking the speckle patterns produced by moving targets has been shown effective for angle independent imaging of blood flow and tissue motion. While speckle tracking overcomes major limitations of Doppler-based flow imaging, the computational complexity of commonly used cross correlation algorithms currently limits it to off-line studies. A much simpler algorithm for angle independent motion imaging is described in this paper. This method requires only one absolute difference operation per pixel, compared to eight operations for normalized cross correlation. Quantitative studies using speckle-generating targets translated by fixed amounts both axially and laterally indicate that the technique tracks moving speckle as accurately as correlation. Color flow images generated from clinical blood and liver data highlight the success of the technique for tracking both large and small motions in two dimensions. The algorithm's suitability for implementation in digital hardware makes possible the development of clinical instruments for angle independent ultrasonic imaging of blood flow and tissue motion in real time.