WP Retina 2x is a Plugin for WordPress which will help us create a user friendly version of our site retina displays, which have a high density of dots per inch and where non-optimized sites are blurred.
The plugin creates the necessary images to be displayed in devices with retina display —At least twice the size of those that will be displayed on normal devices— and detects when our site is accessed from these types of devices, then serving the higher resolution images. In this way we will not waste bandwidth if it is not absolutely necessary.
It is also possible to generate @ 2x images of our entire library at once through the Dashboard. And if a certain image is not large enough to generate the variant for retina screens, the plugin itself will notify us so that we can upload one with a higher resolution. And best of all, it is a free plugin.
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Source and download - WP Retina 2x