sunside

When a user inserts an image using the visual editor, WordPress automatically sets the 
width and height attributes on the image tag. Unfortunately, when the images’ width is 
larger than the CSS “max-width” value, the width is capped but the height is not 
affected, leading to distorted images. 
This plugin either removes all height and width tags from images of a given class 
(resulting in a correct “max-width” behavior) or scales them to a given width to assist 
browsers in creating the layout.
<h3>Known Limiations</h3>
<ul>
<li>Currently, only pixel values are supported when scaling.</li>
</ul>

Proportional Image Scaling

This plugin is an attempt to prevent distorted images when a CSS max-width rule is in effect and the image is inserted using the visual editor.

Kybernetik Services

WP Cool Tools

Martin Stehle

This tiny plugin adds silently the viewport meta tag with zooming permission to allow your users to zoom in your website with mobile browsers.
If you find yourself in trouble not to be allowed to zoom with your favourite smartphone in your theme, you can take this tiny plugin just to get the shiny magic zooming with your smartphone in your theme.
There are themes which are “responsive”. But a few of them are cruel. They do not let you zoom in-to your theme.
Don’t be upset, don’t get in panic, don’t spend a lot of money. Allow mobile zooming definitely in your theme.
You just download this plugin and click to activate it. No options page, no settings. Just your theme.
This plugin does all the magic for you and your users zooming with your smartphone in your theme.
Instead, just adding a second viewport meta line in the header section of a page, I started with version 1.5.0 to add theme specific viewport replacement, if available. 
If you know theme which allows changes in the viewport by a filter, please write a comment in the <a href="https://wordpress.org/support/plugin/definitely-allow-mobile-zooming" rel="ugc">WordPress forum</a> and I will add the specific filter.
If you find yourself in trouble with this tiny plugin, don’t hesitate to ask for <a href="https://wordpress.org/support/plugin/definitely-allow-mobile-zooming" rel="ugc">support</a>.
Try it out on your free dummy site and <a href="https://demo.tastewp.com/definitely-allow-mobile-zooming" rel="nofollow ugc">click here</a>.
The plugin does not collect any personal data, so it is ready for EU General Data Protection Regulation (GDPR) compliance. In your theme.

Definitely allow mobile zooming

This tiny plugin adds silently the viewport meta tag with zooming permission to allow your users to zoom in your website with mobile browsers.

Proportional Image Scaling vs Definitely allow mobile zooming