When a message with multiple images is published to Facebook, only the first attached image will display on the Facebook post. Further, the image must be the first file attached in order to display on the Facebook post: if a non-image file is attached first, and an image file is attached second, the image will not appear on the Facebook post.

To the right is an example of a message with two images attached to it, and beneath is the Facebook post of the message.

Notice that only the first image is visible on the Facebook post. NOTE: Facebook will display the image at a dimension of 158x158 pixels.

A list of supported file types for attachments can be found in the following article: Supported Attachment File Types.