“This 70mm photograph, taken by Astronaut James P. Bagian 16 minutes and 7 seconds after liftoff of Discovery, shows the external fuel tank (ET) against the background of Earth. The tank is falling away from the orbiter following ET separation. The left side shows the burn scar above the solid rocket booster (SRB) forward attach point. The burn is caused by the forward SRB separation motors firing during SRB separation. Post 51-L analysis of the thermal and pressure effects of the separation motor exhaust plume indicate that the scarring is not a safety hazard. However, photographs such as this one were requested for additional missions in order to document the phenomenon and corroborate this conclusion. The photo was made at 15:13:07 GMT, March 13, 1989. It was among the visuals used by the crew at its Mar. 28, 1989 post-flight press conference.”
The above extremely well written & most informative caption is, uncharacteristically, although most appreciatively, at the following:
images.nasa.gov/details-s29-72-059