Adaptive Image | drupal.org

I don't really advocate any of the JS-based image resizing, but there aren't any options short of doing a separate theme, and this at least gets it all handled with a module.

The Adaptive image module provides device-appropriate versions of images from your fields.

You can activate adaptive images by adding an adaptive effect to any of your image styles.

The used technique is derived from http://adaptive-images.com/ by Matt Wilcox.
The hard work is done by Drupal core no need for any additional rewrites.
If image styles work on your website, this module will too.

Hint: Javascript is needed on the clientside to determine the target resolution