janrenz

With Usage of the wordpress.com inofficial webpage to screenshot function this plugins generates screenshots of websites. For more information check http://bdisco.de/wordpress-plugins/ 
There are a few options you can use in your shortcode [webscreenshot]:
url: full Url of the webpage which you want to have screenshoted (mandantory)
width: Pixel width of the screenshot (optional, default: 250)
refresh: If you want to reload the screenshot if it wasn’t generated on the first call (optional, default: true)
link: link image to given url (optional, default: true)
newpage: open link in new page (optional, default: true)
title: set link title tag (will be used as img alt tag also) (optional, default:”)
All img-tags generated will have a class called “webscreenshot”, the link will have a class called “webscreenshot-link” which you can you to perform additional style stuff
Feel free to make pull requests at https://github.com/jprberlin/web-screenshots

Web Screenshots

Displays Thumbnails of a given URL usings wordpress.com inofficial API. Use Shortcode [webscreenshot] with url and some  optional params.

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...

Web Screenshots vs WP-Thumbnail