Im not 100% sure this will fit, because I didnt do this lecture/course, so I dont know the exact method this is made, but if you need free photos you can check unsplash.com
By prompting it with “building front” it gives some nice results (and quite alot of medicore or other purpose pictures). True - they are not straight out textures, so they will require some work in gimp or pshop or any other graphic software, but if you really need that, you might be able to find good pictures.
As a mater of fact, they are not strictly CC0, but Unsplash licence is good enough:
Unsplash grants you an irrevocable, nonexclusive, worldwide copyright license to download, copy, modify, distribute, perform, and use photos from Unsplash for free, including for commercial purposes, without permission from or attributing the photographer or Unsplash. This license does not include the right to compile photos from Unsplash to replicate a similar or competing service.
You can add “texture” to search to get some good results too. But - they always will be only color textures, no normal, bump, roughness od anything like that, so that’s obviously another downside.