Remove width and height from img tag in Drupal output (for certain content type)
function mytheme_preprocess_image(&amp;$variables) {
  foreach (array('width', 'height') as $key) {
    unset($variables[$key]);
  }
}


copy this on template.php (replace "mytheme" to ur theme name) but you need to control over this because it will remove dimensions of all images in your theme.