Won't transport photos- they're all scrambled

I'm a long-time user of iMovie but this has me baffled... if the picture is larger than say 200kb or so the photos won't transport normally into the movie as they're all scrambled. I take photos at about 1704 X 2272 yielding about 1.2 Mb and these photos are all scrambled and won't transport into my movie. Any suggestions from those that like a challenge?