Left and middle panels: running difference images obtained from LASCO C2 observations at 10:24 UT and 12:36 UT on August 22, in which a small propagating blob is shown as a structure with dark center surrounded by bright features (marked by circles in dashed red lines). Right panel: a time-distance map tracking the propagation of the streamer blob in the running difference images. The time starts at 00:00 UT on August 22. The dashed green line denotes the propagation of the streamer blob, from which the tangent derives its propagating speeds. An associated animation is given online.