These images are freely-usable ones from [Unsplash](https://unsplash.com/) and public domain:

- https://unsplash.com/photos/rDEOVtE7vOs
- https://unsplash.com/photos/et_78QkMMQs
- https://unsplash.com/photos/ILip77SbmOE
- https://unsplash.com/photos/95UF6LXe-Lo
- https://www.pexels.com/photo/children-with-her-students-holding-different-color-bells-8535230/