Pete

<p><strong>Note: Obsolete since WordPress 4.4</strong></p>
<p><a href="https://core.trac.wordpress.org/ticket/32230" rel="nofollow ugc">This feature has been added into the core of WordPress 4.4</a>. You can now export your attachments by going to Tools->Export and select ‘Media’ as the export type.</p>
<p><strong>Original Description</strong></p>
<p>WP Attachment Export allows you to export your media library into a WordPress eXtended RSS or WXR file. You can then use the Tools->Import function in another WordPress installation to import the media library.</p>
<h4>Issues / Bug reporting</h4>
<p>Found a bug? Please use the issue tracker at <a href="https://github.com/thehelvetian/wp-attachment-export/issues" rel="nofollow ugc">https://github.com/thehelvetian/wp-attachment-export/issues</a></p>
<h3>Usage</h3>
<p>User <a href="https://wordpress.org/support/profile/philho" rel="ugc">PhiLho</a> has put together a good summary on how to use the plugin at <a href="https://wordpress.org/support/topic/good-but-could-use-more-explanations" rel="ugc">https://wordpress.org/support/topic/good-but-could-use-more-explanations</a>. Thanks PhiLho!</p>


WP Attachment Export

works perfectly.

Exports only posts of type 'attachment', i.e. your media library

MartyThornley

<p>Makes local copies of all the linked images in a post, adding them as gallery attachments.</p>
<h4>Features</h4>
<h4>Credits</h4>
<p>This plugin is baszed on the work done in the “Add Linked Images to Gallery” plugin by http://www.bbqiguana.com/</p>


Import External Images

Funciona perfecto en WP 4.9

Makes local copies of all the linked images in a post, adding them as gallery attachments.

WP Attachment Export vs Import External Images