  Fragile digital watermarking has been applied for authentication and
alteration detection in images. Utilizing the cosine and Hartley transforms
over finite fields, a new transform domain fragile watermarking scheme is
introduced. A watermark is embedded into a host image via a blockwise
application of two-dimensional finite field cosine or Hartley transforms.
Additionally, the considered finite field transforms are adjusted to be number
theoretic transforms, appropriate for error-free calculation. The employed
technique can provide invisible fragile watermarking for authentication systems
with tamper location capability. It is shown that the choice of the finite
field characteristic is pivotal to obtain perceptually invisible watermarked
images. It is also shown that the generated watermarked images can be used as
publicly available signature data for authentication purposes.
