Pinterest isn't all just recipes and fashion - it can be a treasure trove of research for crime fiction authors. I have boards there for my Scott Drayco series research and another for Drayco's world, but also ones for Writing Prompts, Mystery Research, and some "just for fun" boards.
Other authors use Pinterest boards to post images related to their books, like Debbi Mack and her board for her character Sam McRae, Kristi Belcamino with a board on casting her novels, and Laurie R. King on various aspects of her Sherlock Holmes/Mary Russell series.
If you're interested in historical fiction, you can search for information on style and culture of, say, the 1920s or conduct a search on World War II and find images of people, documents, posters, aircraft, even games. Researching archaeology turns up fascinating artifacts and dig sites from around the world, helpful if you're writing a novel on that theme.
Searching for noir novels or pulp fiction novels provides a virtual library of hundreds (thousands?) of classic and not-so-classic covers spanning the history of those genres. Or pick an iconic author like Edgar Allan Poe or Raymond Chandler and there will be quotes, gravesites, childhood photos, movie posters, and the occasional video (and yes, scads of merchandising).
Want to know more about serial killers, past and recent? Or other aspects of true crime? Perhaps you want photos of settings in Edinburgh, from the underground vaults to Edinburgh Castle to pubs. There's also plenty of information, photos, and links about various weapons like Glocks or daggers.
Lest you also think Pinterest is only for women with children (which started out being the social network's core base), the number of U.S. men on Pinterest increased 73% in 2014, and the company says that more men are using Pinterest in the U.S. than read Sports Illustrated and GQ combined (via TechCrunch). Check out these boards from crime fiction authors Ed Lynskey, Lee Goldberg, T.E. Avery, and tech rockstar author Guy Kawasaki.
Plus, Pinterest is the second-largest growing major social network, with a jump of 7% in the past year (just behind Instagram at 9%). So there will continue to be plenty of research opportunities for writers and readers of all stripes. Just be sure and set a timer, because it's easy to fall into the Pinterest universe and get sucked in for hours.