There are a few things you can do to ensure you post a good quality image when sharing on Facebook.
  • The image must be at least 50 pixels in both width and height.
  • The image should not exceed 130x110 pixels. However, larger images will be resized automatically. 
  • The image should not be more than 3 times as wide as tall, or vice versa.
  • If you have a high quality picture that is good but you must save it in a smaller size. When Facebook attempts to shrink the image size to fit into its constraints it makes larger images more blurry.
  • Save the image as a .png file. A .jpg image will work but they are generally less clear when posted on Facebook. This article describes why it is better to use .png.