Adding custom backgrounds is available on these plans. An org admin for the business account can add a custom background by going to Admin Panel > Brand Assets > Backgrounds.
In the backgrounds subtab, you can select header color, font color, and background color — or upload a background image if you prefer (select Image to upload your own background photo).
Custom backgrounds that you create will be added to your Library:
And can then be selected by anyone creating a board on your plan:
For an uploaded background image 2100 px (w) x 1500 px (l) or larger is optimal sizing, but images of at least 1500 px x 1500 px are required to avoid image blur.
A seamless image also works well regardless of the aspect ratio of a particular user's device. But if a seamless background doesn’t make sense, then you may just want your artwork to show up more prominently in the center of the image (so it will be visible regardless of a user's screen size).