How to optimize your images for SEO video lesson explains how to name HTML images and use alt attribute for Google. this video tutorial session shows you how to properly utilize HTML image files to further guide Google to understand web page content.
Google has image publishing guidelines for webmasters which can be located here:
https://support.google.com/webmasters...

Images play a major role in modern website design and also images are a great way to communicate information for relaying your message. Using visual symbols to increase your conversion rates are common strategy that almost all web sites utilize. Although this being the case, and although most of the information regarding image optimization techniques are plentiful on internet, most of them fail to explain how you can and should utilize images so that Google can make the relation between your web page (and the keywords you are targeting) and your images.