<meta property="og:image"
This one drove us crazy for a day or so every thing was fine in the coding of the <meta property="og:image" but we kept getting this error message in the Facebook Debugger Tool
https://developers.facebook.com/tools/debug/"Invalid Image content type"
Turns out the issue was the Height and Width settings on the page the image was on - it was lower than the Minimum image size required by FB o9f 200 px by 200px.
Once we increased it to that the error went away.