There are many great places on the web to find images to use in teaching. Here are some sites that are specific to science.
Access Excellence Graphics Gallery
https://www.accessexcellence.org/RC/VL/GG/
Animal Webcams at the National Zoo
https://nationalzoo.si.edu/webcams
Cells Alive!
https://www.cellsalive.com/
Classroom Clipart: Science Pictures, Photos, Images, and Clipart
https://classroomclipart.com/cgi-bin/kids/imageFolio.cgi?direct=Science
Earth From Space
https://earth.jsc.nasa.gov/
Explore.org Live Nature Cams
https://explore.org/livecams
Eye of Science: Life in a Microcosmic World
https://www.eyeofscience.de/en/
Molecular Expressions Photo Gallery
https://micro.magnet.fsu.edu/micro/gallery.html
National Zoo: Animal Photo Gallery
https://nationalzoo.si.edu/animals/list
Plant Image Gallery
https://nobleapps.noble.org/plantimagegallery/
Sand Atlas
https://www.sandatlas.org/
Welcome to the Planets
https://pds.jpl.nasa.gov/planets/welcome/earth.htm
If you are interested in digital visualization, here are some sites that link to and describe this technology.
Bugscope
https://bugscope.beckman.illinois.edu/
Chickscope
https://chickscope.beckman.uiuc.edu/