Identifying 2 same images using Java

Question

I have a problem in my web crawler where I am trying to retrieve images from a particular website. Problem is that often I see images that are exactly same but different in

Answer 1

calculate MD5s using something like this:

MessageDigest m=MessageDigest.getInstance("MD5");
m.update(image.getBytes(),0,image.length());
System.out.println("MD5: "+new BigInteger(1,m.digest()).toString(16));

Put them in a hashmap.