1. A method for using metadata to detect alteration of audio data, image data, or both, the method comprising: recording a first set of metadata characteristics for a first set of data representing original data, the first set of metadata characteristics including at least one respective semantic description for the first set of data; recording a second set of metadata characteristics for a second set of data representing data under test, the second set of metadata characteristics including at least one corresponding semantic description for the second set of data; comparing the first and second sets of metadata characteristics wherein, in the event the first and second sets of metadata characteristics are not identical, then the second set of data is identified as an altered version of the first set of data, and performing the comparing by comparing the first and second sets of metadata characteristics to identify one or more of: at least one location in the first set of data that have been altered, or at least one metadata characteristic that has changed from the first set of data to the second set of data, wherein the at least one metadata characteristic that has changed is identified using the at least one semantic description for the first set of data and the at least one corresponding semantic description for the second set of data; and at least one metadata characteristic that has changed from the first set of data to the second set of data is identified using the at least one semantic description for the first set of data and the at least one corresponding semantic description for the second set of data, the method further comprising using the identified at least one metadata characteristic to define a change of semantic meaning between the first set of data and the second set of data, determining whether or not the defined change of semantic meaning changes an overall meaning of a message defined by the first set of data and, if so, generating an alert indicative of a possible criminal intent in altering the message corresponding to the first set of data.