The theme of this tidbITS is working with photographs and pictures. These programs are perfect for gathering and editing nature photos!
pixabay.com: Free high-quality images
Pixabay.com offers images and videos released free of copyrights under Creative Commons CC0. You may download, modify, distribute, and use them royalty-free for anything you like, even in commercial applications.
When using pixabay, skip past the Sponsored Images at the top, which will have watermarks on them, and instead use the free images underneath.
PicMonkey.com is a free site for editing images. Use PicMonkey to upload a picture and make alterations to color and size, add effects, include a frame, and more! You can upload multiple images to make a collage. This tool can help students visualize information.