My photos are high quality jpg images. When you try to put some of the images in iMovie, they become blurry. Not all of them, but just some of the photos. I deleted my preferences, and still have the problems. In some cases, they will also just be a black image, and it doesn't recognize the image at all.
I've used iMovie for years, and never had these types of issues before. You can only use about 2/3 of the photos, all taken with the same camera, a Nikon. I also tried to make a trailer, that won't let me drop in any photo. So the trailer is useless. It runs, but then there are 3 seconds of blackness as it won't take any image in my photo database.
I was perfectly happy with iMovie until the latest version became available. For the "what's new in iMovie", I just wish they'd make it useable.