code: def get_key(self, path, geometry, filters, options):
          
          seed = u' '.join([
              str(path),
              str(geometry),
              str(filters),
              str(options),
          ]).encode('utf8')
          return md5(seed).hexdigest()
docs: Generates the thumbnail's key from it's arguments.
          If the arguments doesn't change the key will not change