title: Unique image hash that does not change if EXIF info updated
body: <p>I'm looking for a way to create a unique hash for images in python and php.</p>
  
  <p>I thought about using md5 sums for the original file because they can be generated quickly, but when I update EXIF information (sometimes the timezone is off) it changes the sum and the hash changes.</p>
  
  <p>Are there any other ways I can create a hash for these files that will not change when the EXIF info is updated? Efficiency is a concern, as I will be creating hashes for ~500k 30MB images.</p>
  
  <p>Maybe there's a way to create an md5 hash of the image, excluding the EXIF part (I believe it's written at the beginning of the file?) Thanks in advance. Example code is appreciated.</p>