Could you explain in more details what you mean by this, cause it can mean many things, like background image behind header theme part, or some people call header the title of article. I need more info :-)
Anyway if it is "background image behind header theme part" then you set it in Customizing ▸ Header settings▸ Type, variant, background but only for vertical header.
If you mean image in article title bar, then edit page -> Page details and there check option for Title bar and Featured media.
Comments
Could you explain in more details what you mean by this, cause it can mean many things, like background image behind header theme part, or some people call header the title of article. I need more info :-)
Anyway if it is "background image behind header theme part" then you set it in
Customizing ▸ Header settings▸ Type, variant, background but only for vertical header.
If you mean image in article title bar, then edit page -> Page details and there check option for Title bar and Featured media.
With kind regards.