I have an image stored as Blob in data store in google appengine (python) .. i want to upload this image to a server .
1- what is required to be done to upload this stored image to the server ?
If the API that you are dealing with wants to have a URL from which to fetch the image, what you can do is set up a handler that will serve the image from the blob.
The AppEngine Docs lay out what you need to do in your code. Is there something specific about those instructions that you don't understand?