描述：

通过id获取缩略图(特色图像)的图片信息

用法：

<?php wp_get_attachment_image( $attachment_id, $size, $icon, $attr ); ?>

参数：

$attachment_id

(integer) (必填) 附件ID

默认值: None

$size

(string/array) (可选) 图像大小。字符串关键字（缩略图、中、大或全）或以像素表示宽度和高度的两项数组，例如数组（32,32）。从2.5版起，此参数不影响媒体图标的大小，媒体图标始终以其原始大小显示。

默认值: 'thumbnail'

不要使用需要检查所有图像大小的数组，应该考虑使用add_image_size注册大小，以便生成裁剪版本。它比找到最接近的图像更有效.

$icon

(boolean) (可选) 使用媒体图标表示附件。

默认值: 'False'

• 1 (True)
• 0 (False) - 默认

$attr

(string/array) (可选) 查询字符串或属性数组。

默认值: None

示例：

<ul>
<?php if ( have_posts() ) : while ( have_posts() ) : the_post();    

 $args = array(
   'post_type' => 'attachment',
   'numberposts' => -1,
   'post_status' => null,
   'post_parent' => $post->ID
  );

  $attachments = get_posts( $args );
     if ( $attachments ) {
        foreach ( $attachments as $attachment ) {
           echo '<li>';
           echo wp_get_attachment_image( $attachment->ID, 'full' );
           echo '<p>';
           echo apply_filters( 'the_title', $attachment->post_title );
           echo '</p></li>';
          }
     }

 endwhile; endif; ?>
</ul>

源文件：

/**
 * Get an HTML img element representing an image attachment
 *
 * While `$size` will accept an array, it is better to register a size with
 * add_image_size() so that a cropped version is generated. It's much more
 * efficient than having to find the closest-sized image and then having the
 * browser scale down the image.
 *
 * @since 2.5.0
 *
 * @param int          $attachment_id Image attachment ID.
 * @param string|array $size          Optional. Registered image size or flat array of height and width
 *                                    dimensions. Default 'thumbnail'.
 * @param bool         $icon          Optional. Whether the image should be treated as an icon. Default false.
 * @param string|array $attr          Optional. Attributes for the image markup. Default empty.
 * @return string HTML img element or empty string on failure.
 */
function wp_get_attachment_image($attachment_id, $size = 'thumbnail', $icon = false, $attr = '') {
	$html = '';
	$image = wp_get_attachment_image_src($attachment_id, $size, $icon);
	if ( $image ) {
		list($src, $width, $height) = $image;
		$hwstring = image_hwstring($width, $height);
		$size_class = $size;
		if ( is_array( $size_class ) ) {
			$size_class = join( 'x', $size_class );
		}
		$attachment = get_post($attachment_id);
		$default_attr = array(
			'src'	=> $src,
			'class'	=> "attachment-$size_class",
			'alt'	=> trim(strip_tags( get_post_meta($attachment_id, '_wp_attachment_image_alt', true) )), // Use Alt field first
		);
		if ( empty($default_attr['alt']) )
			$default_attr['alt'] = trim(strip_tags( $attachment->post_excerpt )); // If not, Use the Caption
		if ( empty($default_attr['alt']) )
			$default_attr['alt'] = trim(strip_tags( $attachment->post_title )); // Finally, use the title

		$attr = wp_parse_args($attr, $default_attr);

		/**
		 * Filter the list of attachment image attributes.
		 *
		 * @since 2.8.0
		 *
		 * @param array        $attr       Attributes for the image markup.
		 * @param WP_Post      $attachment Image attachment post.
		 * @param string|array $size       Requested size.
		 */
		$attr = apply_filters( 'wp_get_attachment_image_attributes', $attr, $attachment, $size );
		$attr = array_map( 'esc_attr', $attr );
		$html = rtrim(" $value ) {
			$html .= " $name=" . '"' . $value . '"';
		}
		$html .= ' />';
	}

	return $html;
}