How Facebook processes your photos
Facebook stores photos at fixed widths — 720, 960 or 2048 pixels — and re-compresses everything to keep pages fast. Upload a size its pipeline doesn't expect and you get scaling plus harsh re-encoding stacked together, which is where the smeared look comes from.
Uploading at exactly 2048 px on the long edge, already cleanly compressed, gives the pipeline a file it can pass through with minimal damage. That's this page's preset.
Sizes that matter on Facebook
| Placement | Recommended size |
|---|---|
| Photo posts (best quality) | 2048 px long edge |
| Link preview image | 1200 × 630 |
| Cover photo | 851 × 315 (displays 820 × 312 desktop) |
| Profile picture | ≥ 320 × 320 (shown small) |
| Event cover | 1200 × 628 |
Sharing to a website instead? Facebook link previews use your page's og:image — 1200 × 630 under ~1 MB renders fast and crisp. Compress it on the website images page.