Here is an idea I had:
Request apis from all major stock photo websites, free, like Pixabay, Pexels, Gratisography etc. and also ones that cost money like shutterstock, dreamstime etc. This will work as a very slick and easy to navigate directory for these stock photo sites. Spend a little money to get a website layout that with the objective of having the most efficient way of sorting through images. As a user of free stock photo sites, I know that people will appreciate the new big players of free stock photos being rounded up in the same place. This is something I would hope to see happen in the future and suspect it will come about soon so why not make it your idea.