An encoder transforms at least a portion of a signal, counts the resulting
transform coefficients having a zero value, and encodes the signal with
the zero count. A decoder decodes the signal in order to recover the zero
count. The decoder may also determine its own zero count of the signal as
received and may compare the zero count that it determines to the
recovered zero count. The decoder may be arranged to detect
compression/decompression based upon results from the comparison, and/or
the decoder may be arranged to prevent use of a device based upon results
from the comparison.