The reason we use the present tense to describe a person in a photo or a video, is similar to the reason that we use the present tense when we are discussing or criticizing the actions in a novel or a play, but sometimes the past continuous is correct as in the example that follows.
For example, in discussing the play Hamlet we would generally use the present tense: Hamlet investigates the sightings of the ghost of his father. Later, he finds a skull in a graveyard that he grimly jokes is of a court jester that he knew when he was younger. That is, before the actions of the play begin. Hamlet does not realize that the grave that is being dug is likely for Ophelia.
Generally, the present tense is correct for discussing fiction such as in the example from Study.com where the story of the tortoise and the hare is explicated:
'The fast hare challenges other animals to a race. The slow and steady
tortoise accepts the challenge. The hare, who is confident in his
abilities, decides to take a nap on the course. As a result, he
Since the present tense is used to discuss poems, stories, novels, plays, it follows that the present tense should also be used for film and video, and also for photographs and paintings.