how to perform the watermarking with cryptography?

 hi....
      I want to embedded an encrypted watermark to a cover medium and to evaluate the quality of extracted watermark after decryption...The watermark embedding must be in DCT domain. How should I write the code for performing this operation? Anybody having the code for reference?

[Geoff Hayes]

Which is line 96?

[neetha k k]

d=bitxor(op,r); error during this operation

[Geoff Hayes]

You may want to review this decryption code

 for i=1 :256
    for j=1:256
       d=bitxor(op,r);
    end
 end

What is r, as it hasn't been defined previously? What is the data type for op? Note also that this loop doesn't do anything different on each iteration as it just repeats the same bitxor operation without making use of the indices i and j. (As an aside, you should name these indices to something else because i and j are also used as representations for the imaginary number.)

[Neethu]

I just want to encrypt the watermark before embedding to the cover image.Also decrypt it after the extraction...what should i do for that? can you please help me

[Geoff Hayes]

Neethu - you need to explain what your code is attempting with the decryption. Why have you written it this way?

Answer 1

[Image Analyst]

If op is uint8, then r must be uint8. If op is uint16, then r must be uint16. It does not let you mix integer types when doing operations on them together. In other words, if op is uint8 and r is uint16, it won't allow that. Your code is more than I want to take the time to read and understand, so it's up to you to figure out what integer type they are and what you need, and make them match. You can use the functions cast(), typecast(), uint8() and uint16() to do any necessary conversion(s).

Answer 2

[Neethu]

hi.... I want to embedded an encrypted watermark to a cover medium and to evaluate the quality of extracted watermark after decryption...The watermark embedding must be in DCT domain. How should I write the code for performing this operation? Anybody having the code for reference?

[Image Analyst]

There are tons of papers on watermarking here: http://www.visionbib.com/bibliography/contents.html