function add_tags_to_attachments() {
    register_taxonomy_for_object_type( 'post_tag', 'attachment' );
}
add_action( 'init' , 'add_tags_to_attachments' );

function category_and_tag_archives( $wp_query ) {
    $my_post_array = array('post','page','attachment');
 
    if ( $wp_query->get( 'category_name' ) || $wp_query->get( 'cat' ) )
    $wp_query->set( 'post_type', $my_post_array );

    if ( $wp_query->get( 'tag' ) )
    $wp_query->set( 'post_type', $my_post_array );
}

function inserted_image_titles( $html, $id ) {
	$attachment = get_post($id);
	$thetitle = $attachment->post_title;
        
        $tags_str = '';
        $tags_array = wp_get_post_tags($id);
        foreach ($tags_array as $tag) {
            $tags_str .= $tag->name.' ';
        }
        if($tags_str != '') {
            $tags_str = substr($tags_str, 0, strlen($tags_str)-1);
        }
	$output = str_replace('<img', '<img title="'.$thetitle.'"', $html);
        
        if(strpos($output, 'alt=""')===false) {
            $output = str_replace('" width', ' '.$tags_str.'" width', $output);
        } else {
            $output = str_replace('alt=""', 'alt="'.$tags_str.'"', $output);
        }
        
        return $output;
}
add_filter( 'media_send_to_editor', 'inserted_image_titles', 15, 2 );

function featured_image_titles($attr, $attachment = null){
	$attr['title'] = get_post($attachment->ID)->post_title;
        
        $tags_str = '';
        $tags_array = wp_get_post_tags($attachment->ID);
        foreach ($tags_array as $tag) {
            $tags_str .= $tag->name.' ';
        }
        if($tags_str != '') {
            $tags_str = substr($tags_str, 0, strlen($tags_str)-1);
        }
        $attr['alt'] = (($attr['alt']=='')?'':$attr['alt'].' ').$tags_str;
	return $attr;
}
add_filter('wp_get_attachment_image_attributes', 'featured_image_titles', 10, 2);