Presumably that’s one use of the IMAGE RECORD section on a tricorder (TNGTM, p. 121):
This section manages single or sequential image files recorded by the standard tricorder. The control has four divisions: FORWARD, REVERSE, INPUT, and ERASE. When used in concert with other tricorder functions, relatively complete documentation of an away mission can be achieved. At standard imaging resolution, at a normal recording speed of 120 Area View Changes (AVC)/sec, the tricorder can store a total of 4.5 hours of sequential images. Higher speeds yield a proportionately lower total recording time.