You can't just "Google it" when searching for images to use in presentations. Most images are copyrighted and to use them we need to ask permission first and then give the owner credit. Here are some websites to find public domain, free-to-use images. Because the internet is ever changing, it is always important to check the site out before sending students to it. One option (especially for younger students) is to search for the images, save, and share with students in Seesaw, Google Classroom, or another workflow tool. Another option is to have students take their own pictures.
Be sure to check the site and the image to be sure of the guidelines for use.