knuten

This plugin let you add a shortcode with two different image sources one too a normal sized image and one for retina. The plugin will then load the right image depending on if it’s a retina display or not. 
For more info and how to use it.
<h3>A brief Markdown Example</h3>
<pre><code>[retina normal="path-to-normal-image" retina="path-to-retina-image" width="image-width" height="image-height" /]
</code></pre>

Retina for WP

This plugin let you add a shortcode with two different image sources one too a normal sized image and one for retina.

Matthew Haines-Young

The new srcset attribute has recently dropped in Chrome and Firefox. It is the simplest way to get retina ready images on your site.
This plugin will automatically add the srcset attribute to your images if a suitable retina sized image can be found.
It also includes a JS polyfill – <a href="https://github.com/scottjehl/picturefill" rel="nofollow ugc">Picturefill</a> – to ensure that this works on all browsers – not just those that support srcset. This is about 6.5kb, and can easily be dequeued if you only wish to support browsers that have implemented this functionality.
This plugin does not handle generation of the alternative images, and this should either be done manually or using another plugin. See installation instructions for more information.
This plugin requires PHP 5.3

WP Srcset

Very simple plugin to get retina images on your WordPress site. Automatically load high resoloution images using the new srcset attribute.

Retina for WP vs WP Srcset