7. A computer program product for annotating a stimulus, the computer program product comprising a non-transitory computer usable medium having computer readable program means for causing a computer to perform the steps of: detecting a plurality of facial expressions in an audience of the stimulus; interpreting the facial expressions to estimate a mood for a time period of the stimulus, wherein interpreting the facial expressions comprises: classifying each of the facial expressions as corresponding to an emotion from a set of emotions; and statistically analyzing the respective emotions corresponding to the plurality of facial expressions to estimate the mood; generating an annotation of the stimulus based on the mood estimated; repeating the detecting, interpreting, and generating steps to produce a plurality of the annotations that respectively correspond to different time periods of the stimulus; and indexing the annotations according to the respective moods, wherein the indexing provides a two-way linkage between the annotations and the time periods of the stimulus.
7. A computer program product for annotating a stimulus, the computer program product comprising a non-transitory computer usable medium having computer readable program means for causing a computer to perform the steps of: detecting a plurality of facial expressions in an audience of the stimulus; interpreting the facial expressions to estimate a mood for a time period of the stimulus, wherein interpreting the facial expressions comprises: classifying each of the facial expressions as corresponding to an emotion from a set of emotions; and statistically analyzing the respective emotions corresponding to the plurality of facial expressions to estimate the mood; generating an annotation of the stimulus based on the mood estimated; repeating the detecting, interpreting, and generating steps to produce a plurality of the annotations that respectively correspond to different time periods of the stimulus; and indexing the annotations according to the respective moods, wherein the indexing provides a two-way linkage between the annotations and the time periods of the stimulus. 8. The computer program product of claim 7 , wherein the stimulus comprises an audio-video stimulus.