The presently claimed invention relates generally to content identification, such as deriving identifiers from content itself. One claim recites a method including: using a processor, deriving first information from audio elements of an audio signal; using a processor, deriving second information from data representing picture elements of a video signal that is associated with the audio signal; and utilizing the first information or the second information in a content filtering process, said process utilizes a recognition unit or device to sample content being distributed on a network, and controls further distribution of the content in the network based at least in part on the first information or the second information. Of course, other combinations and claims are provided as well.