code: def instance_ik_model_receiver(fn):
      
      @wraps(fn)
      def receiver(self, sender, **kwargs):
          # print 'inspect.isclass(sender? %s'%(inspect.isclass(sender))
          if not inspect.isclass(sender):
              return
          for src in self._source_groups:
              if issubclass(sender, src.model_class):
                  fn(self, sender=sender, **kwargs)
  
                  # If we find a match, return. We don't want to handle the signal
                  # more than once.
                  return
      return receiver
docs: A method decorator that filters out sign_original_specals coming from models that don't
      have fields that function as ImageFieldSourceGroup sources.