1. A method of training an automated classifier to identify categories of content items of a content set using a device comprising a processor and having access to at least one human classifier, the method comprising: executing on the processor instructions configured to: for respective content items of the content set: using the automated classifier, identify at least one category for the content item with a classification confidence; for respective content items having a classification confidence below a classification confidence threshold: send the content item to a human classifier, and upon receiving from the human classifier at least one category associated with the content item, store the content item in a training set associated with the at least one category; and train the automated classifier using the training set.