9. The computer-implemented method of claim 1 , further comprising: for a first one of the verified labels: forming a training set of candidate volumes to which the first one of the verified labels has been assigned; and training a classifier using the determined features of the candidate volumes in the training set, the classifier configured to receive a candidate volume and to output a score indicating a degree of likelihood that the candidate volume contains a representation of the verified label.
9. The computer-implemented method of claim 1 , further comprising: for a first one of the verified labels: forming a training set of candidate volumes to which the first one of the verified labels has been assigned; and training a classifier using the determined features of the candidate volumes in the training set, the classifier configured to receive a candidate volume and to output a score indicating a degree of likelihood that the candidate volume contains a representation of the verified label. 10. The computer-implemented method of claim 9 , further comprising: identifying a volume in a digital video; obtaining a score by applying one of the trained classifiers to the volume; and responsive to the score having at least some given threshold value, adding the label corresponding to the classifier to video metadata of the video.