Apple iMovie

Ok, I'm in school and using my teachers apple laptop to make a slideshow with iMovie, and I have the whole thing done, but the quality of the pictures is shitty. like you can't even see them well cause they are so blurred. They are high quality photos, and they were saved at high quality on her computer. but when I put them in the program, they suck. is there some setting that changes this, or does Iphoto or Imovie resize automatically? anyone who knows macs help me out!