Only after reading your post, I found a link labelled "Change Background Image" effectively camouflaged on the bottom left of the page, but this only allows me to select an alternative but equally obtrusive image.
There does not appear to be any immediate way to eliminate the background image entirely and revert to the clean, usable design that I expect from Google.
After you change the background image, the words change to 'Remove background image' which seems unintuitive since it puts the first background image back up.
Only after reading your post, I found a link labelled "Change Background Image" effectively camouflaged on the bottom left of the page, but this only allows me to select an alternative but equally obtrusive image.
There does not appear to be any immediate way to eliminate the background image entirely and revert to the clean, usable design that I expect from Google.