Thumblink

Thumblink automatically creates thumbnails for all of your blog posts to make your links look better. A link to your WordPress site on platforms like Facebook, Twitter, and LinkedIn is often the first interaction you have with a visitor.
Every link’s thumbnail is 3x larger than its text preview – if it looks ugly or unmaintained, your page loses a potential visitor. Thumblink automatically generates these thumbnails by taking a screenshot of each page.
The Thumblink WordPress plugin relies on the <a href="https://thumblink.com" rel="nofollow ugc">Thumblink</a> service in order to generate thumbnails. Please read Thumblink’s <a href="https://thumblink.com/tos" rel="nofollow ugc">TOS</a> and <a href="https://thumblink.com/privacy" rel="nofollow ugc">Privacy Policy</a> prior to installation.

Thumblink automatically generates thumbnails for every page on your website to make your links look better.

Kemory Grubb

Book Previewer enables you to use a shortcode to retrieve and display Google Books previews of titles you specify. To use the shortcode, you must have an International Standard Book Number (ISBN), Online Computer Library Center (OCLC) ID, Library of Congress Control Number (LCCN), or Google Play Generated Key (GGKEY) for the title you want to display. Additionally, a Google Books preview of that title must exist.
Features:
<ul>
<li>Uses a shortcode and the Google Books Embedded Viewer API to display a free preview for a book you specify</li>
<li>Includes a “Book Preview” widget that can be used in place of the shortcode</li>
<li>Includes a text editor button that enables you to insert the majority of the shortcode without typing</li>
<li>Supports WordPress localization (i18n)</li>
<li>Supports displaying the preview as an embedded page element, a popup, or a direct link to the title on the Google Books site</li>
<li>Supports site performance protection mechanisms, including caching of elements and an option to defer loading until the page footer</li>
</ul>

Book Previewer

Retrieve and display Google Books previews for an ISBN, OCLC, LCCN, or GGKEY you specify on any WordPress page or post.

Thumblink vs Book Previewer