What are the major differences between robust and a fragile

What are the major differences between robust and a fragile watermarking? Give an example application where each of these techniques is useful.

Solution

Robust watermarking:-
should be stuck to the document it has been embedded in, in such a way that any signal transform of reasonable strength cannot remove the watermark. Hence a pirate willing to remove the watermark will not succeed unless they debase the document too much to be of commercial interest. The latter form is the very challenging and attracts most research.
example- it is use in CD/DVD copy prevention.

Fragile Watermarking:-
should be able to detect any change in the signal and identify where it has taken place and possibly what the signal was before modification. It serves at proving the authenticity of a document

example:- it is used in image copy prevention