Filter IMG tags when displaying posts and pages to remove WIDTH & HEIGHT attributes and replace with CLASS attribute.
TxTu Set Image Class is a WordPress plugin. The plugin is a filter for images found on your WordPress posts / pages. Before displaying a post or page on your WordPress blog, it will search for images (identified by the tag). It will then remove any height, width or align attributes found on the image. Depending on your setting, it will insert class and id attributes in the images