Where should I get creative-commons licensed photographs?

This is by far the best collection. It has an api too : https://source.unsplash.com

You can try pexels: https://www.pexels.com/. If you need their API, you will need to email them. Here's the page where you can get more info on their API: https://www.pexels.com/api/

This is a little like pexels but they try to filter out the low quality images through AI. It searches across the leading paid and free providers. You can find out about their api here: https://api.everypixel.com/