How to move movie files from iMovie library to Photos library
Solution 1:
Find the Imovie Library
In finder navigate to the Imovie Library file. It should be in this directory Users/NAME/Movies/iMovie Library
. Right click the and select Show Package Contents.
Find the right event
There you'll find a directory for each event. Each event directory contains a folder called original media. Those files can be dragged into Photos.