Add .img-responsive class to all images uploaded/added in WordPress

add-img-responsive-class-images-wordpress.php

<?php

/**
 * @desc Add .img-responsive to all post images ~mj
 */
function add_post_img_responsive_class($attr) {
	$attr['class'] .= ' img-responsive'; // note the leading space
	return $attr;
}
add_filter('wp_get_attachment_image_attributes', 'add_post_img_responsive_class');

/**
 * @desc Add .img-responsive to all editor images
 */
function add_editor_img_responsive_class($class) {
	$class .= ' img-responsive'; // note the leading space
	return $class;
}
add_filter('get_image_tag_class', 'add_editor_img_responsive_class');