2. The method of claim 1 , wherein selecting a final label for the non-text content item comprises: identifying one or more n-grams for each of the different label groups, each n-gram including one or more words from initial labels that are included in the different label group; determining, for each identified n-gram, a number of the different label groups for which the n-gram was identified; and selecting, as a final label for the non-text content item, an identified n-gram for which the number of different label groups meets the threshold number of different label groups.
1. A method performed by data processing apparatus, the method comprising: identifying a non-text content item that is associated with each of a plurality of web pages; receiving label data that includes a set of initial labels for the non-text content item, wherein each initial label includes one or more words; grouping, for each of two or more sets of matching web pages among the plurality of web pages, initial labels that are associated with the set of matching web pages into a label group, the initial labels for different set of matching web pages being grouped to different label groups; grouping different sets of matching labels from the set of initial labels into different label groups; and selecting, as a final label for the non-text content item, an n-gram of one or more words that is included in at least a threshold number of different label groups.