get_attached_media()

Hi all,
There is post with images ( inserted by “add Media” ). I want to get attached images - I use this:

$media = get_attached_media( ‘image’ );
print_r( $media );

And I have got empty array.
It look like this images is not attachment to this post. And I try to do the same for video - It look like video is not attachment to post too.

What is attachment for posts?

I have found answer:
I can’t get images if they are already in media library.
I can get images if they are new - I load it from my computer to media library and after that attach it to post.