In Japan, there are numerous illustrated field guides (図鑑 or "zukan" in Japanese). Many of them are for kids and provide illustrated looks at things like dinosaurs, bugs, or trains. Then, there are zukan that are drawings guides—drawing guides for adults.

These adult zukan feature women (or men) in various nude poses. Many of them claim to be artist desk references and not all of them feature nudity (check this gun zukan with improper weapon handling).

A newly released one, Multi-Angle Pose Collection: A Nude Field Guide for Anime, features ladies dressed as game characters like the girls from Konami's Love Plus games or a Mami Tomoe from anime Puella Magi Madoka Magica. Did I just say dressed? Ha, silly me. They're not really dressed. But there are multiple angles.

A couple of the models—Kokomi Naruse and Ayumu Sena—are actually adult video actresses. So while these books claim to be photo guides, they often seem more like collections of adult pictures. But that's probably the the point.

The photos in the above gallery have some of the more adult elements taken out. However, they still might not be work safe.

マルチアングルポーズ集 アニメのためのヌード図鑑 [Amazon Japan]