Add Css class to img from media uploader

Add Css class to img from media uploader

<?php
/**
* Add Css class to img from media uploader
*/
class media_uploader_cb{
	
	function __construct(){
		// attach our function to the correct hook
		add_filter('attachment_fields_to_edit',  array( $this, 'attachment_fields_to_edit' ), 10, 2);
		//save attachment field
		add_filter( 'attachment_fields_to_save', array( $this, 'attachment_fields_to_save' ), 10, 2);
		//add custom css class
		add_filter( 'media_send_to_editor',      array( $this, 'media_send_to_editor' ), 10, 2 );
	}

	/**
	 * Adding our custom checkbox field to the $form_fields array
	 * 
	 * @param array $form_fields
	 * @param object $post
	 * @return array
	 */
	function attachment_fields_to_edit($form_fields, $post) {
		$form_fields['add_class']['label'] = __("Add CSS Class");
		$form_fields['add_class']['input'] = 'html';
		$form_fields['add_class']['html'] = '<input type="checkbox" value="1" name="attachments['.$post->ID.'][add_class]" id="attachments['.$post->ID.'][add_class]" '.checked( 1, get_post_meta($post->ID, 'add_class', true), false ).'/>';
		return $form_fields;
	}


	/**
	 * Saving our custom checkbox field
	 * @param array $post
	 * @param array $attachment
	 * @return array
	 */
	function attachment_fields_to_save($post, $attachment) {

		if( isset($attachment['add_class']) ){
			update_post_meta($post['ID'], 'add_class', $attachment['add_class']);
		}
		return $post;
	}

	/**
	 * Adding our custom css class based on checkbox field 
	 * 
	 * @param string  $html
	 * @param int $id
	 * @return string
	 */
	function media_send_to_editor( $html, $id ) {
		//only add class if the checkbox was checked
		if ( 1 == (int)get_post_meta($id, 'add_class', true) ){
			//change this to whatever you want
			$css_class_to_add = 'img-responsive';
			//check if it has class attribute 
			if (false === strpos( strtolower( $html ), 'class="') ){
				//it has no class attribute lets add our class to it
				$html = str_replace('<img', '<img class="'.$css_class_to_add .'"', $html);
			}else{
				//it has class attribute lets add our class to it
				$html = str_replace('class="', 'class="'.$css_class_to_add . ' ', $html);
			}
		}
		return $html;
	}
}

new media_uploader_cb();