Abstract: In an automatic speed monitoring system of the type in which data is incorporated into a photograph of a vehicle, security of the data is provided through the addition of redundant information to the recorded data. The data is processed to derive an alphanumeric test symbol that is based on the data symbols. This test symbol is recorded along with the data. In subsequent validation of the data, the data is processed in the same manner to derive a symbol, and this symbol is compared with the recorded test symbol to determine the correctness of the recorded data.