1. Apparatus for use with a portion of a subject's body that assumes a plurality of different shapes, the apparatus comprising: an image-acquisition device configured to acquire a plurality of image frames of the portion of the subject's body; a display; and at least one computer processor, configured to: receive the image frames, designate at least one of the image frames as a first baseline image frame, a shape of the portion in the first baseline image frame being designated as a first baseline shape of the portion, identify the portion within a first non-baseline-shape image frame of the plurality of image frames, the portion not being shaped in the first baseline shape within the first non-baseline-shape image frame, deform the first non-baseline-shape image frame by deforming the shape of the portion in the first non-baseline-shape image frame, such that the shape of the portion becomes more similar to the first baseline shape of the portion than when the portion in the non-baseline-shape image frame is not deformed, form at least a first composite image that is of higher clarity with respect to anatomy of the portion, relative to each of the acquired image frames, by averaging at least the deformed first non-baseline-shape image frame with the first baseline image frame, and drive the display to display the first composite image.