From lurid drawings of television characters in erotic poses to more accomplished, atmospheric portraits of fictional favourites, online fan art is now the way many devoted viewers express their appreciation. Like its literary equivalent, fan fiction, popular shows such as Doctor Who, Sherlock, Peaky Blinders and Fleabag have inspired thousands of amateur artists to upload work. Many of the images are also sent to the actors.

Mandip Gill, who stars as Yasmin Khan opposite Jodie Whittaker’s Doctor in Doctor Who, spoke recently of her surprise at the avalanche of fan art she has seen since she has played the part in the BBC show. “It is amazing,” Gill said. “And we all look so cute in most of it.”

Last week, fresh evidence came from America that some fan artists are trying to influence not only plot development but major casting decisions. A painting depicting Keanu Reeves as Mister Sinister in the Marvel Cinematic Universe’s X-Men series was shared online in an attempt to persuade producers to look in Reeves’s direction in the future. The Marvel villain, also known as Nathaniel Essex, has already been mentioned in the films X-Men: Apocalypse and Deadpool 2, but he has yet to make a live-action appearance.

Fan art has grown from homespun creative trend to wider commercial uses: artwork inspired by a succession of Doctor Who episodes has been published in book form; BBC One heralded the return of Peaky Blinders last year with an amateur art competition, entered by more than 1,000 fans. Now organisers of leading “Comic Con” events, such as the one to be staged in London in February, are allocating larger areas for galleries to sell this creative work to other fans.

Artists can pay £80 to set up a small stall, alongside comic book creators, in an Artist Alley at London Olympia to promote their original work while they sketch. The annual event in the capital is attended by a line-up of acting talent from leading film and television series and is run by Showmasters, who also stage similar Comic Cons in Cardiff, Sheffield, Exeter and Bournemouth. More than 90,000 visitors are expected to attend the Olympia event.

Fan art, like fan fiction, is wildly varied, but much of it has a close stylistic relationship with the Japanese manga cartoon tradition, and with “cosplay”, the popular teenage hobby of dressing up as fictional characters. Some of the work is also derived from American comic book illustrations, or from the gothic graphics associated with prog rock or heavy metal music.

Actors Cillian Murphy – Tommy Shelby in Peaky Blinders – and Benedict Cumberbatch – Sherlock Holmes in Sherlock – are popular subjects in fan art and fan fiction. Cumberbatch has spoken of the dubious impact of amateur Sherlock stories and of the visual images that focus on the sleuth’s imaginary sexual encounters with sidekick John Watson. Cumberbatch’s 2016 role as Dr Strange in the Marvel film has also prompted an outpouring of drawings and fiction, and the actor has performed written passages for comic effect.