There is default one that is in /styles/master1/c/ folder. If you want to replace it, just upload image with "caption-sub.jpg" name to the folder. Size should be 1920 x 320 pixels (6:1)
You can use Caption Image field in CMS to replace it on specific pages.
Or upload Category Image on category pages.
1. CMS - "Header" field
2. Ecommerce Category - category name
3. Ecommerce Product - product name
4. Blog list - blog name
5. Blog post - post name
6. News/Events item - news/events name
Subtitle
Blog and News/Events module also contain subtitle that is pushed automatically from modules
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SEO Content appears the first in source code and on the very bottom of page. Its placement depends on Module.
1. Edit it in CMS "SEO Content" Content Area on normal CMS pages.
2. E-commerce categories have it in "SEO ("SEO Content")" section.
3. E-commerce Product is editable in "SEO Data (Content)" section.