This plugin will add Semantic Tagging functionality to Annotorious: while typing an annotation, the text is sent to a server for Named Entity Recognition. Recognized entities are suggested as possible tags, and the user can add them to the annotation by clicking on them. Tags are Semantic Tags in the sense that they are not only strings, but (underneath the hood) include a link to their corresponding DBpedia entry.
Sample image source: Hallstatt, Austria, by Nick Csakany/Wikimedia Commons. Public Domain.