In November, we launched Instant Previews to help users better understand if a particular result was relevant for their search query. Since launch, our Instant Previews team has been keeping an eye on common complaints and problems related to how pages are rendered for Instant Previews.
When we see issues with preview images, they are frequently due to:
- Blocked resources due to a robots.txt entry
- Cloaking: Erroneous content being served to the Googlebot user-agent
- Poor alternative content when Flash is unavailable
To help webmasters diagnose these problems, we have a new Instant Preview tool in the Labs section of Webmaster Tools (in English only for now).
Reference link:http://googlewebmastercentral.blogspot.com/2011/05/troubleshooting-instant-previews-in.html