The front page (also known as the homepage) has four image sections that you can customize. They each come with a default image you can use on your site or for testing. To upload your own images, just click on the Upload button.
A great resource to find free high resolution photos is unsplash.com
Note: The image sections will appear when content is added to the front page widgets which are found in Appearance > Customize > Widgets.
Recommended photo images sizes:
Welcome Section: 2000px wide & 900px high
Call to Action Section: 2000px wide & 650px high
Content Block 1 Section: 2000px wide & 900px high
Content Block 2 Section: 2000px wide & 1100px high
These sections are very versatile in that you can also use graphic patterns that repeat, create opacity filters for a monochrome look or solid colored backgrounds.
Options on Image Sections:
Background Size: Cover, Contain, 100% Width, 100% Height, Actual Size
Background Horizontal Position: Left, Center, Right
Background Position Vertical: Top, Center, Bottom
Overlay Color: Select an overlay color for the image
Background Overlay Opacity: Choose the opacity value for the overlay color.
(0 = transparent | 1 = solid ) Use the slider to change the value.
Typical setting for a background image: No Repeat, Cover, Center, Center plus your desired overlay color and opacity (if any).