said 1 year, 2 months ago:
@barbc that’s a strange one, I haven’t seen anything like that. Something you could try is go to this site http://lorempixel.com/ and double click the dimensions to change them and use the 851×315 pixels and then click on the color or gray image. You’ll be given a random image that is exactly the size you entered. Then right click the image to save it to your computer.
See if uploading one of their images has the same effect.
My guess without being right at your computer is there may be something in the exif data with the image, or for some reason FB isn’t reading the file properly.