How can we embed a watermark into the roi?

Suppose we find all the possible roi in an image using some feature detector and now we nee to embed a watermark in a particular roi. Then how can we do it?

[Walter Roberson]

duplicates http://www.mathworks.co.uk/matlabcentral/answers/104803-can-we-use-a-binary-mask-to-embed-a-watermark-in-the-roi