Robo

WP-Thumbnail is a simple and neat WordPress Plugin that not only allows you to use a short-code to generate dynamic 
screenshot of webpages in your posts but also takes a realtime snapshot of the served webpage and saves a link to it 
on the page itself that too without burdening the servers. This helps in optimizing search results on Google by adding 
a thumbnail to the left of the search result snippet and makes shared posts more attractive, with a relevant thumbnails, 
on Social Sites like Facebook.
For more information, check out <a href="http://wp-thumbnail.robocasters.com/" rel="nofollow ugc">wp-thumbnail.robocasters.com</a>.
Features include:
<ul>
<li>Short-Code – The plugin has a shortcode that enables you to add dynamic screenshots of webpages to your post.</li>
<li>Meta Thumbnail – It uses meta name thumbnail and adds the live screenshot in it for being displayed as a thumbnail in Google Searches.</li>
<li>PageMaps – PageMaps is a structured data format that provides Google with information about the data on a page. It enables website creators to embed data and notes in webpages.</li>
<li>Facebook OG:Image – It sets image with content og:image to the top priority for being used as a Facebook Post thumbnail.</li>
<li>WP-Thumbnail Class – It adds a WP-Thumbnail class that helps image to be used for all other sharing purposes.</li>
</ul>

WP-Thumbnail

'Changing the way you share', giving you an experience you have never had before...

Thomas Schulte

This plugin dynamically shows preview screenshots of hyperlinks as tooltips on your WordPress site.
For the tooltip effect a jQuery plugin called “qTip2” is used internally. 
Find more about this great project here: http://qtip2.com/ 
The thumbnails are provided by http://thumbsniper.com and its API.

ThumbSniper

This plugin dynamically shows preview screenshots of hyperlinks as tooltips on your WordPress site.

WP-Thumbnail vs ThumbSniper