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Make your images responsive by defining rules for switching ImageCache presets based on CSS media queries.
This module allows administrators to define rules that replace one ImageCache preset by another when a media query is being evaluated. On content load and viewport resize all the defined rules will be evaluated and image src attributes will be replaced to point to the correct imagecache preset. While there are better alternatives for implementing responsive images this works well for quick & dirty replacements with minimal configuration.
Please note that this module is not suitable for large sets of images.
There is currently only a drupal 6 version available. For Drupal 7 there are several alternatives available, e.g. Responsive images and styles.