1. A method for real-time motion correction in compound ultrasound imaging, said method comprising: receiving a new image frame; updating a frame buffer with said new image frame, said new image frame replacing an oldest image frame in said frame buffer; applying spatially variant shading to frames in said frame buffer; estimating motion between said new image frame and a previous image frame in said frame buffer to form an estimated motion, said new and previous image frames including spatially variant shading; updating stored motion information with said estimated motion, said stored motion information describing motion between all frames to be used to construct a compounded image; aligning image frames in said frame buffer to said new image frame based on said updated motion information; and forming a compound image from said image frames in said frame buffer.