Okay, I am building a website that is accessible using the keyboard. However there are some pages where there is no focus-able content - no links, forms or buttons. When the users presses the TAB key (after skipping the navigation). He jumps straight to the footer.
Am I supposed to add Tabindex="0" to headings and images or do users just use the arrow keys in situations like this?
Looks like it's fine as it is. You don't need to tab over headings and images as long as they are not interactive. HTML5 was created to provide semantics that, when used properly, will keep things predictable. Adding tab indices will only make things unpredictable. Keyboard users will scroll to see and read the content. For visually impaired people there is assistive technology (screen readers) that give them shortcuts to navigate over every relevant and accessible element on the page. So headers and images (at least with alt text) won't be missed. Screen readers even allow for quick scanning landmarks on the page like headers and menu's etc.
Testing the page for keyboard users is easy, just try it yourself. Here is an overview of keystrokes. Screen reader testing requires a little more effort but can be done with NVDA for Windows which is free, or VoiceOver for MacOS which is standard on every Mac.
