Medium writers are stuck between a rock and a hard place when it comes to images. They really only have a couple of sources of free images like Unsplash and Pixabay. Gone are the days when you could get good stock photography for $.99 an image. Only the top writers here pay for stock images. I do see a lot of images that are unattributed which are clearly not been paid for or aren't from Unsplash. If you want to stand out and make the money, I would pay for your images on Shutterstock or iStock.