Delivering optimized images to your WordPress site is essential when viewing from lower bandwidth, smaller mobile device. It makes sense to deliver smaller images to mobile devices to speed up loading times and have happier viewers.
Plus, WordPress is an awesome platform to build on, and with the rise of responsive theme design, it is necessary to find a solution to deliver these responsive images.
The plugin is loaded via your themes 'functions.php' file. Next, add some function calls to include mobile image sizes for the standard WordPress sizes, as well as adding your own sizes for custom images around your theme.
Now wherever you need an image, simply call the relevant Responsage function to deliver the appropriate size for mobiles and desktops. This can be adapted for featured images, gallery images and an image shortcode.
You can check out Responsage in action on the premium WordPress theme Allure (change the browser user agent string to a mobile device to view the resized images).
Responsage is currently a plugin to include within a theme. So if you are a theme developer and want to easily implement responsive images, download and install Responsage into your theme. Responsage utilizes standard WordPress functions, so it won't interfere with other plugins you may have installed.