how to hard code an image into a page template

In most template files you should use the full URL of the image, and not the relative path.

Bad:

<img src="image.jpg" />

Good:

<img src="https://mysite.com/wp-content/theme/images/image.jpg" />

There’s various functions that can help with getting the URL, but start off looking at get_template_directory_uri() (for main or parent themes) and get_stylesheet_directory_uri() (for child themes).