django replace old image uploaded by ImageField
This might get tricky, 
And a lot of times depends on what are your constraints. 
1. Write your own save method for the model and then delete the old image a and replace with a new one. 
     os.popen("rm %s" % str(info.photo.path))

Write a cron job to purge all the unreferenced files. But then again if disk space is a issue, you might want to do the 1st one, that will get you some delay in page load.
How I can replace one image uploaded by an ImageField (in my models) with the new one selected by the same ImageField?
And, can I delete all images uploaded by an ImageField when I delete the model object (bulk delete)?