Unfortunately, you didn't specify which schools you need to write about, but it seems to me that in any case there are many images on the Internet. If you care about the quality of images then use the portal that you were advised. This portal is one of the most famous and has been around for a very long time.

I'm glad you're starting to write blogs about different schools now. And I understand you because once too was engaged in blogging and find a site with good pictures is very difficult. But fortunately, I found a site where you can find organizing images https://depositphotos.com/stock-photos/organizing.html that clearly will not disappoint you. I hope you enjoy this site and you will use it regularly.