title: Add text string to an image file using Python
body: <p>I have a set of GIF files in which I need to insert a specific string at anywhere inside the binary file but it should not be visually different. I could probably do it in an hex editor but not sure where, as it may corrupt the file.</p>
  
  <p>This is a requirement by by my source control system where it is checked for "$Header $" string in each file before they are checked in.</p>
  
  <p>I have many files so need to do this using python. </p>