Drupal image resize

add class to img
class="img-responsive" alt="Responsive image"


img {max-width: 100%; height: auto;}

or add to theme
<?php
/**
*
*/
function THEMENAME_preprocess_image_style(&$vars) {
$vars['attributes']['class'][] = 'img-responsive'; // http://getbootstrap.com/css/#overview-responsive-images
}
?>