Some time ago I had this bright idea that I would make my photographs available as stock photography. These days, with sources like iStock, that's a relatively easy thing to do. What I didn't realize are the rules that restrict the kind of photos iStock (and I assume other agencies) is and is NOT interested in accepting.
“No pictures of the artist's shadow!” the rule demanded. I never knew so many photographers photographed their own shadow. I do it most every day, so that eliminated about 5,000 of my images. Never-the-less, I was fascinated that iStock felt so strongly about this. NO SHADOWS. They will accept just about every other cliche known to imaging, except maybe pet pictures. NO SHADOWS, NO PET PICTURES! A guess a shadow of your pet would ban you from iStock for life.
This soured me on stock photography forever and haven't been back to iStock, nor shall I visit them or their silly rules again. And I'm still photographing my shadow.