The file size seems way to small compared to the number of graphics, and I recently lost a bunch of images (suddenly replaced with empty box with an icon and three dots in the corner). The images were added by pasting from clipboard screen captures.
Hello,
if Edit -> Link to External Files... is greyed out, none of the images within your presentation is linked but all are embedded. Pasting from the clipboard embeds images (which is also the default action using Insert -> Image ... if you don’t tick option [x] Insert as Link explicitly.
If Edit -> Link to External Files... is not greyed out, select the menu item and you get a list of linked Images and their respective location on your filesystem.
I don’t have such a menu item. I’m using version 5.3.6.1. I do have one called “link…” which is grayed out.
… and you did not mention your version. Anyway - I got no other answer