Thumbnail policy → Guide to images → Image cheat card → User images → Video policy → File naming conventions → Video recommendations → Gallery → Galleries and slideshows/wikitext → Untransmitted images → Ogg format banned → Header image → Images and perspective
Like text, images have a point of view. It's important to match their point of view with the perspective of the article as a whole.
For in-universe articles, images must come from an in-universe source, such as a screenshot of a televised episode, or a scan of a comic strip. Novel or audio covers may also be potential sources for in-universe imagery, but only when no other source has a satisfactory image to offer, particularly if they are "floating heads"-style covers rather than an illustration of a specific event in the plot.
Promotional images — such as when actors pose in costume for a picture — are specifically disallowed. A good rule of thumb for determining whether an image of a TV character is a screenshot or a promotional image, is that if the character is looking directly into the camera, the picture is probably promotional and thus cannot be used on in-universe articles. Such pictures may be used on real world articles about the actor pictured, but out-of-costume pictures are preferred on such pages.
This ruling specifically means that most wallpapers available from the BBC's official website are not allowed on in-universe pages here. In fact, the best use for promotional images on this site is in maintenance images, such as are found on stub templates and the site's background images.
Out-of-universe and story articles
For story articles, promotional images also should not be used. Instead screenshots that capture "iconic" scenes from the story should be used.
Promotional images mainly belong on pages about an actor or other behind-the-scenes staff member. Even so, a picture of an actor out of costume is preferred over one with the actor dressed in character.
Note that just as promotional images should not be used on DWU pages, screenshots should be avoided on real world pages. If you don't have a headshot or other promotional image to go on an actor's page, don't put up an image at all. It is better that the article about, say, Bernard Horsfall go without a picture than to reuse the picture which is on display at Goth.
Put simply, the actor isn't the character, so don't use a picture of one to illustrate the other.