Hi, @opopop!

Thanks for posting your question!

In case you have the latest version of Photo Gallery (1.3.44/2.3.44), please create/edit a gallery and press Import from Media Library button to import images into your gallery.

But if you have an older version, please follow these steps. Go to Photo Gallery Options > Global Options > General tab and enable Import from Media Library option. You will see a new button appearing in Photo Gallery’s image uploader, titled Media Library. You can use it to import images.

Let me know in case you have further questions.
Thanks! Have a great day!