Add filler graphic based on custom field

I’m currently building a site at https://falcon.schuminweb.info/ as a conversion to WordPress of my regular site at https://www.schuminweb.com/. On the main page, I display a photo feature that fills most of the page. When the image is oriented horizontally, it fills the allocated space nicely. When the image is oriented vertically, it is too narrow and needs some filler material in order to make things look right.

Thus what I’m trying to do is tie the presence or non-presence of some HTML code to create the filler material into a custom field. Thus if the value of custom field “photofeature_vertical” is equal to 1, the filler material displays. Any other value in that slot, or if the custom field is not used at all, will render different code that omits the filler.

I’m sure there’s a clean, elegant way to do this, but my hunt through Google hasn’t come up with anything. Any ideas how to accomplish this?