First-time setup

Do these five things once. Then most articles will share correctly.

1. Open System - Easy Meta (see the previous tab).
2. On the first tab, leave Enable Easy Meta and Overwrite existing social tags set to Yes.
3. Click the Images tab.
4. Click Fallback image and pick a picture from Media. A wide photo works well (about 1200 by 630 pixels).
5. Leave Generate 1200 by 630 JPEG on Yes if your server has GD.
6. Click Save (top toolbar).
7. Open System > Clear Cache and delete the cache.

That fallback picture is used when an article has no intro image of its own.