When you conduct a search on Google, there is a link just above the search query results that says "Show Options." Clicking on that link will display a left sidebar to provide filters for the search results before you. The filtering options include: images, videos, dates, etc.
Google has been committing serious investment in its Books program--from legal defense to the purchase of companies that own potential enhancement technologies.
The latest update for Google's Book program is the introduction of the filter "Books" under "View options" filtering tools.