A good friend and critique partner just started an ICL course and wrote a story inspired by a picture prompt. She found the experience a little frustrating because she has so many ideas of her own that she wants to work on. However, she worked on it and will learn from the experience, I'm sure.
Earlier, I was browsing some pictures I'm considering for my website and they sparked something. In fact, they helped me over a mental hurdle in the story I wanted to write. The concept and characters were there, but I couldn't put the pieces together. Less than an hour after my image browsing, I had a rough draft typed and formatted. It's not the way I usually write, but images can be powerful inspiration.
If you're interested in finding free public domain images, check out
Wikimedia Commons, but be sure to check out specifics for each photo.
Another good sources is
OpenClipArt, but if you search
Creative Commons, it searches several search providers at once. Be sure to check the specifics for each photo.
Finally, for many people, paying for royalty-free stock photos may be the way to go. One service that gives users a 7-day free trial is
deposit photos. Just be aware of the trial period and be sure to cancel before the trial is over if you don't find it as useful as you had hoped.
Happy Searching!