Abstract:
With the availability of some powerful image processing
softwares such as ‘Adobe Photoshop’, one can remove/replace
some features in a picture easily without any detectable trace. This
type of operation may be regarded as tamper. However, in some
cases, a person or an organization cannot afford an image to
undergo any such operation, such as images for military, medical or
judicative use etc. The validity and authenticity of an image is of
utmost importance in such cases, so there is a need to guarantee
the integrity of an image in an effective manner. Also in the second
phase, one must be able to localize and identify an area which has
been tampered or has developed some sort of an error while
passing the transmission channel or during storage/retrieval
process.
This thesis presents an image authentication and error
localization technique, based on fragile water marking. The
watermark is content based and the error localization method uses
a “Cyclic Redundancy Checksum” to authenticate image as well as
localize any channel induced or intentionally introduced error, down
to block level (2x2 pixels). The scheme has been tested on various
image formats as well as image sizes and has successfully
localized error/tampering with good PSNR valves.
