Can I change the 404 error image?

Add a custom image for the 404 and 500 error system pages in theme settings (no code required)

From Theme Settings, click System Pages:

Expand the Error 404 settings and change the dropdown to Custom Image:

Replace 404 Error Image

The default image on the 404 page is 751 px x 290 px but you can create an image using whatever size works best for your page layout design.

Optimize with tinypng to reduce the file size without impacting the quality. 

Choose PNG or WebP for optimal loading, you can also use JPEG or GIF.