描述：

通过id判断一篇文章是否为图片附件

用法：

 <?php wp_attachment_is_image( $post_id ); ?> 

参数：

$post_id

(int) (可选) ID

默认值: 0

源文件：

/**
 * Checks if the attachment is an image.
 *
 * @since 2.1.0
 * @since 4.2.0 Modified into wrapper for wp_attachment_is() and
 *              allowed WP_Post object to be passed.
 *
 * @param int|WP_Post $post Optional. Attachment ID. Default 0.
 * @return bool Whether the attachment is an image.
 */
function wp_attachment_is_image( $post = 0 ) {
	return wp_attachment_is( 'image', $post );
}