Upload the school's cover photo. Owner/admin only. PNG/JPEG/WebP, max 8MB.

PUT /branding has always taken cover_image_url, which is the right shape for a school that has its banner on its own web server and the wrong one for every other school — a coordinator has a JPEG, not a URL, and until this existed the only way to set a cover was a seeding script (see seed_demo_school.seed_branding, which says so). The logo had an upload and the cover did not, so half the branding screen could not be operated by the person it is for.

Flattened onto white and capped at 1600px wide: the same "what every student downloads" argument the logo's 512px cap is made of, one order of magnitude up because this one is a photograph.