1. A method for imaging a portion of a body of a subject that undergoes motion, the method comprising: using an image-acquisition device, acquiring a plurality of image frames of the portion of the subject's body; using at least one processor, identifying a feature in at least some of the image frames; using the processor, image tracking the at least some image frames with respect to the feature, by aligning the at least some image frames with respect to the feature; displaying on a display, as a stream of image frames, the image frames that have been image tracked with respect to the feature; and using the processor, at least partially reducing visibility of a periphery of the displayed stream of image frames.