Downloading images from your Google Docs documents is a bit tricky or in other words not easily assomplishable.
One very quick and efficient way how to do it is to actually convert the Google Docs document into a web format.
Check out tutorial: Converting Google Docs document into a web format
Once you’ve converted the document into a web format, open up the web document and simply save the images by the browser’s right click and choosing Save image as
Hope this helps. 😉