Hey Lincoln,Welcome to JustAnswer!You're chatting to Pete.
I'll be happy to assist with your iMovie question today.
First, close iMovie then try trashing the preferences file for iMovie. Relaunch iMovie and the preferences file will be recreated.
Let me know if the photos now appear normally again...
You should be using iMovie 10 with El Capitan??
Please go to the Apple logo at the upper left of your computer screen to About This Mac and give me this information: