可以使用插件：

http://wordpress.org/extend/plugins/download-shortcode/

虽然它不是特定于WP的，但以下是如何强制用户下载图像：

if ( $attachments = get_posts( array(
    \'post_type\' => \'attachment\',
    \'post_mime_type\'=>\'image\',
    \'numberposts\' => -1,
    \'post_status\' => \'any\',
    \'post_parent\' => $post->ID,
) ) );
foreach ( $attachments as $attachment ) {
    echo \'<a href="javascript:void(0);"
        onclick="document.execCommand(\\\'SaveAs\\\', true, \\\'\' . get_permalink( $attachment->ID ) . \'\\\');">
        Download This Wallpaper</a>\';
}

将以下内容另存为image.php 关于您的主题：

<?php

// This forces all image attachments to be downloaded instead of displayed on the browser.
// For it to work, this file needs to be called "image.php".
// For more info, refer to the wp hierarchy diagram.

// Get the path on disk. See https://wordpress.stackexchange.com/a/20087/22510
global $wp_query;
$file = get_attached_file($wp_query->post->ID);

// Force the browser to download. Source: https://wpquestions.com/7521
header(\'Content-Description: File Transfer\');
header(\'Content-Type: application/octet-stream\');
header(\'Content-Disposition: attachment; filename=\'.basename($file));
header(\'Content-Transfer-Encoding: binary\');
header(\'Expires: 0\');
header(\'Cache-Control: public\'); //for i.e.
header(\'Pragma: public\');

// ob_clean(); // Looks like we don\'t need this
flush();
readfile($file);
exit;