I know the URL of an image on Internet.
e.g. http://www.digimouth.com/news/media/2011/09/google-logo.jpg, which contains the logo of Google.
Now, how can I download this image using Python without actually opening the URL in a browser and saving the file manually.
Here is a more straightforward way if all you want to do is save it as a file:
import urllib
urllib.urlretrieve("http://www.digimouth.com/news/media/2011/09/google-logo.jpg", "local-filename.jpg")
The second argument is the local path where the file should be saved.
As SergO suggested the code below should work with Python 3.
import urllib.request
urllib.request.urlretrieve("http://www.digimouth.com/news/media/2011/09/google-logo.jpg", "local-filename.jpg")