Digital Image Archive is an alternative place to find images of U.S. National Parks. You can search the archive by park and or subject. All of the images are free to download as they are in the public domain.
The National Parks Service also offers a b-roll video gallery. The videos in the galleries are in the public domain. The b-roll video gallery can be searched by park, monument, building, or person. All of the videos can be downloaded. Some files are quite large so keep that in mind if your school has bandwidth limits and you have all of your students searching for videos at the same time.
Applications for Education
The NPS Digital Image Archives could be a good resource for students to access when they need scenic imagery to use in slide presentations, in video projects, or in image-based stories created with tools like Pic-Collage, PicMonkey, and ThingLink.