One Crayon

Markup to Featured Image will automatically generate a featured image when you publish a post, with the intent of allowing you to publish posts with featured images from third-party clients like MarsEdit.
To add a featured image to your post, include one of the following markup variants in your post’s content:
<pre><code><img src="/path/to/image.jpg" data-featured-image="keep" />
<img src="/path/to/image.jpg" data-featured-image="strip" />

</code></pre>
If you use an <code><img></code> element, the values of the <code>data-featured-image</code> attribute specify whether the image should be displayed when the post is shown on your site (<code>keep</code>) or ignored when the post is displayed (<code>strip</code>). The order of attributes in your <code><img></code> tag (and whether you include other attributes, like width/height, title, alt, etc.) doesn’t matter. You can make it as complicated or simple as you like.
If the post already has a featured image, the plugin will do nothing (version 1.0 does not allow updating the thumbnail by updating the markup).

Markup to Featured Image

Automatically set the featured image (formerly the post thumbnail) for a post based on custom markup in the body text.

cubecolour

Add the [zoom] shortcode to a page, post or custom post-type post. If the post has a featured image it will displayed on the page, and when you move the cursor over the image, the image will be magnified with the image viewport remains constrained to the dimensions of the original image.
on a mobile/touch device the image will also be zoomable, but as there is no hover state this is achieved by means of a pinch & zoom action.
On my site you can see a <a href="https://cubecolour.co.uk/featured-image-zoom/" title="demo of Featured Image Zoom" rel="nofollow ugc">demo</a> of the plugin.
<h4>Usage:</h4>
Ensure that your post/page has a featured image defined.
Use a [zoom] shortcode to your page.
Some optional shortcode parameters can also be used.
=size= 
The large image is used by default for the unzoomed image. Use the size parameter to use a different defined image size.
eg ‘[zoom size=thumbnail]’
=zoomsize= 
The full image is used for the zoomed overlay. This can be changed using the zoomsize shortcode parameter.
eg ‘[zoom zoomsize=large]’
The image size definitions used for the the unzoomed and zoomed images should have the same aspect ratio and cropping.
=zoomin= 
This can be used to tweak the level of zoom. The value must be a positive integer. The default is 6 so if the zoom level results in too much magnification on hover, try a lower value.
eg ‘[zoom zoomin=2]’

Featured Image Zoom

Add a [zoom] shortcode to display a zoomable featured image.

Markup to Featured Image vs Featured Image Zoom