Random Image

I especially like to use this instead of a slider. I hate sliders. But with this, each page load is a different image. Link

Fluid Gallery

This uses the flexbox superior layout model just like my themes. Link

MrKDilkington - Full Screen Background Image and Overlay

This has a number of cool options for your background image. Use it. Link

Background Image Slideshow

Use this for a series of images on your background page. Just like the static image above but this displays a series of images you select. Link

Image with Focuspoint

Very cool! This image block is perfect for use with FoxyBox. You can set the image to be just the size you need so that your content always looks beautiful. Link