I'm using Django / Python. After saving the model I want to make a screenshot (preview) of how it looks in the template and save it on model field. Please tell me how to do it.
Not sure how you actually want it to work. You can however use the following links to pass a url and fetch its screenshot:
http://www.programmableweb.com/api/shotbot
These are the third party applications which work just fine. You can try them.