A method comprising: receiving an image stream; determining when a specialized classifier can be used to classify a subset of multiple aspects of content of the image stream, the specialized classifier exploiting class skew of the subset of the multiple aspects, the determining including identifying when the subset of the multiple aspects dominates the image stream based on a cumulative distribution function of the classes resulting from classifying the input stream by a general classifier; accessing the specialized classifier to classify the subset of the multiple aspects subsequent to determining that the specialized classifier can be used; using the specialized classifier to classify the subset of the multiple aspects in subsequent images of the image stream; the method characterized by determining when usage of the specialized classifier is to cease based on statistics associated with the classification results; changing to using the general classifier to classify the subset of the multiple aspects in images of the image stream subsequent to the determination that usage of the specialized classifier is to cease; wherein the determining when the specialized classifier can be used further comprises: predicting how long the class skew of the multiple aspects will last by analyzing the previous class skews from the image stream and their duration; and determining that the specialized classifier can be used to classify the subset of the multiple aspects in response to the class skew being predicted to last at least as long as an amount of time that accessing the specialized classifier to classify the subset of the multiple aspects is expected to take. receiving an image stream; determining when a specialized classifier can be used to classify a subset of multiple aspects of content of the image stream, the specialized classifier exploiting class skew of the subset of the multiple aspects, the determining including identifying when the subset of the multiple aspects dominates the image stream based on a cumulative distribution function of the classes resulting from classifying the input stream by a general classifier; accessing the specialized classifier to classify the subset of the multiple aspects subsequent to determining that the specialized classifier can be used; using the specialized classifier to classify the subset of the multiple aspects in subsequent images of the image stream; the method characterized by determining when usage of the specialized classifier is to cease based on statistics associated with the classification results; changing to using the general classifier to classify the subset of the multiple aspects in images of the image stream subsequent to the determination that usage of the specialized classifier is to cease; wherein the determining when the specialized classifier can be used further comprises: predicting how long the class skew of the multiple aspects will last by analyzing the previous class skews from the image stream and their duration; and determining that the specialized classifier can be used to classify the subset of the multiple aspects in response to the class skew being predicted to last at least as long as an amount of time that accessing the specialized classifier to classify the subset of the multiple aspects is expected to take. predicting how long the class skew of the multiple aspects will last by analyzing the previous class skews from the image stream and their duration; and determining that the specialized classifier can be used to classify the subset of the multiple aspects in response to the class skew being predicted to last at least as long as an amount of time that accessing the specialized classifier to classify the subset of the multiple aspects is expected to take.