iMovie doesn't move any photos over but relies heavily on iPhoto Library and where the actual photo is stored. If this goes corrupted - iMovie get's lost too.
And - there can be a mismatch of Thumb-nail photos and the actual photo.
I would close iMovie and all other applications - Then Start iPhoto - BUT KEEP DOWN alt-key and cmd-key during up-start then select all repairs from the list.
THIS WILL TAKE HOURS - so have lot's of time to do this - AND if LapTop - KEEP MAINS ADAPTOR connected so that You don't run out of battery.
Yours Bengt W