I write Seven Wordses on 3×5 Index cards. Sometimes landscape (wide) and sometimes portrait (high). Facebook seems to have a lot of trouble sizing (and shaping) images to display, mainly – I think – due to a misguided insistence on cropping them rather than re-sizing them. With pictures, it’s not always glaringly apparent, but with text, cropping cuts off whole lines or edges and renders the text unreadable. Here’s a Gallery of cards – let’s see what it looks like.
So there’s the top image of I think 12 images. Maybe – if it works – the thing to do is to always put a landscape image first, or use a featured image, in landscape format.