specially I want to extract hidden information from a bank note to detect counterfeit bank note. How can I do this ? please help.
Well, converting an image to binary is easy enough. You can use im2bw http://www.mathworks.com/help/images/ref/im2bw.html
As for extracting hidden information, you're really going to have to give us more to work with. What kind of hidden information are you looking for?