Here are requirements for using Facebook images in Shack Open Graph:

• The minimum allowed image dimension is 200 x 200 pixels.
• The size of the image file must not exceed 8 MB.
• Use images that are at least 1200 x 630 pixels for the best display on high-resolution devices. At the minimum, you should use images that are 600 x 315 pixels to display link page posts with larger images.
• If your image is smaller than 600 x 315 px, it will still display in the link page post, but the size will be much smaller.
• the aspect ratio for images is the same across desktop and mobile Newsfeeds. Try to keep your images as close to the 1.91:1 aspect ratio as possible to display the full image in Newsfeeds without any cropping.
• The Facebook crawler only accepts gzip and deflate encodings, so make sure your server uses the right encoding.