Upload a full-page website screenshot. It opens full-width in the browser, with no extra address bar, and is processed in HD so it stays sharp.
For best quality: capture the full page as PNG at 2× resolution. In Chrome: F12 → Ctrl+Shift+M → set DPR to 2 → ⋮ menu → “Capture full size screenshot”. Or use the “GoFullPage” extension and save as PNG. Don't upload a screenshot of a screenshot, a WhatsApp-compressed image, or a video frame; those are already blurry.