Have you enabled Google enhanced image search?

Do you have a blog where only images speaks? or
you have a blog posts more with images than content? or
Worried why your site article or pages are not much indexed with Google Search?

Here is the reason why you need to opt-in enhanced image search!

If you enable enhanced image search, Google will use tools such as Google Image Labeler to associate the images included in your site with labels that will improve indexing and search quality of those images. So make sure you have proper tooltips or alt or title in image tag which describes the image, to know more about alt and title just go through this cool article on the “alt” and the “title” attributes by 456 Berea Street.

Google Enhanced Image Search, is an opt-in tool which is available to all webmasters at Google Webmasters Central

How to enable it?

• Go to Google Webmasters Central.
• Click on Get started > Improve traffic with Google Webmaster Tools > Learn More.
• Login with your Google account, now you should be in Dashboard, select the site for which you want to enable Google enhanced image search.
• Then click on Tools > Enable enhanced image search.

Follow the instructions given and enable the same.
That’s it you are done, the rest Google will take care :)

Source: Google Support