Why does the wrong image appear on Facebook when I post a page?

If you post a page to Facebook and have specified an image but find Facebook shows a different one, it's likely that your  image is too small.

Facebook require the specified image to meet their minimum size guidelines. If your image is too small, they will attempt to choose another one that appears on the same page that is large enough.

As their guidelines can change from time to time, we recommend checking out these resources for up-to-date information:

If you correct the image and re-share the same page URL, Facebook may still continue to show the incorrect image, because they store a copy in their cache.

To clear their cache, submit your page URL in their Debugger tool. It will show you what they currently know about your page, and you should be able to click a button labelled Scrape Again. This will update their cache and fetch your new image.

A default image for Facebook can be specified in Site Settings, in the  Images and Icons section. However, this will only ever be used if you don't specify a specific Facebook image for a page. If this image is also too small it wont be used, and Facebook will pick another image from the page.