There are 2 global options related to header image.

Select header type to be global (all pages, all posts, all properties, all agents, all taxonomies, all archives and categories)

and Enable parallax for all header media with image or video

 

If you wish to use header image only for a specific page / post / property / agent / use this option and you have more images options

Parallax effect applies if your image height is larger than 300px