WP AJAX random image widget

random-image-widget.js

jQuery(document).ready(function($) {
  $.post(ajaxurl, {action:'random_image_widget'}, function(feedback){
    image = jQuery.parseJSON(feedback);
    img = $('<img src="'+image.thumb+'" />');
    $('.widget_equesrandomimagewidget').append(img);
    $(img).wrap('<a href="'+image.full[0]+'" width="'+image.full[1]+'" height="'+image.full[2]+'"></a>');
    Shadowbox.setup(img.parent());
  });
});

random-image-widget.php

<?php

class RandomImageWidget extends WP_Widget {
	function __construct() {
		parent::WP_Widget( false, $name = 'Random Image Widget', array('description' => 'Displays a random image from the blog') );
		if( ! is_admin() && is_active_widget(false, $this->id, $this->id_base) )
			wp_enqueue_script('random-image-widget', plugin_dir_url(__FILE__).'random-image-widget.js', array('jquery'), null);
	}

	function register() {
		return register_widget('RandomImageWidget');
	}

	function widget($args, $instance) {
		extract($args);
		$title = apply_filters('widget_title', $instance['title']);
		echo $before_widget;
		if ( $title )
			echo $before_title . $title . $after_title;
		echo '<div class="random-image-widget"></div>';
		echo $after_widget;
	}

	function update($new_instance, $old_instance) {
		return $new_instance;
	}

	function form($instance) {
		$title = esc_attr($instance['title']);
		?>
			<p><label for="<?php echo $this->get_field_id('title'); ?>"><?php _e('Title:'); ?> <input class="widefat" id="<?php echo $this->get_field_id('title'); ?>" name="<?php echo $this->get_field_name('title'); ?>" type="text" value="<?php echo $title; ?>" /></label></p>
		<?php 
	}

	function ajax() {
		global $wpdb;

		$page_arr = $wpdb->get_col( "SELECT ID FROM $wpdb->posts WHERE post_type = 'page'" );
		$pages = implode( ',', $page_arr );

		$attachment_id = $wpdb->get_var( "SELECT ID FROM $wpdb->posts WHERE post_type = 'attachment' AND post_mime_type = 'image/jpeg' AND post_parent NOT IN ($pages)" );

		if ( ! $attachment_id )
			die();

		echo json_encode( array( 'full' => wp_get_attachment_url( $attachment_id ) ,'thumb' => wp_get_attachment_image_src( $attachment_id, array(215,500) ) ) );

		die();
	}
}

add_action( 'widgets_init', array('RandomImageWidget','register') );
add_action( 'wp_ajax_random_image_widget', array('RandomImageWidget','ajax') );
add_action( 'wp_ajax_nopriv_random_image_widget', array('RandomImageWidget','ajax') );