CAPNTHLA is an acronym for "Completely Automated Public NetHack Test to tell 'Hackers and Losers Apart". It is a highly specialized form of CAPTCHA.
This is the only type currently extant. The user is presented with the name or a description of an item class, dungeon feature or monster and is required to input the ASCII character used to represent it in the default configuration of NetHack. This slightly discriminates against tiles users, but seems to be fairly effective.
- Dudley's Dungeon requires users to pass an item/feature CAPNTHLA before rating strips or posting comments.
- The Bilious PatchDB requires users to pass an item/feature CAPNTHLA before rating patches or posting comments.
- This wiki, when registering a new user, and when editing not logged in. (using mw:Extension:QuestyCaptcha)
- The NetHack Quote Database, when submitting a quote.