title: PHP creation of signature
body: <p>I am thinking of a way to create digital signatures. I need this because some files needed to be signed like certificates by a authorized user and the receiving user must see it is from a authorized and also in case of disputes the issued user must verify it is his file.</p>
  
  <p>For that I am trying to upload an image with actual signature inside the image.</p>
  
  <p><strong>Question:</strong> Can i get unique values from the signature image?</p>
  
  <p>I am thinking to get unique value from the image and then give to the <code>openssl_sign</code> with an encrypted form of unique values from the signature image as the private key.</p>
  
  <p>By this the issuing user can sign and also verify the file it is his. But the receiving user will require a key to open the file.</p>
  
  <p><strong>Question:</strong> Can i give key to user(a key that is only available to receiving user) to open that encrypted file?</p>
  
  <p>I have searched but had trouble finding these things. Please explain these things and please give a better idea if my logic is wrong.</p>
  
  <p>Thanks</p>