A Story uses a tall viewing area, so a vertical source is often easier to prepare than a wide scene. Before exporting, look at what will disappear from the sides of a landscape photograph. If the important people or objects span the whole width, a forced tall crop may be the wrong way to present the image.
Our preset exports 1080×1920 pixels, a 9:16 JPEG. Those dimensions describe this tool's output. They do not guarantee a fixed unobstructed area in every version of Facebook's Story interface. Names, controls, captions, and other overlays can occupy space around the image. Keep the subject away from boundaries that may be covered, then inspect the actual composer.
If the whole source must stay visible, make a finished vertical design with the intended background in your image editor first. This tool does not add borders, automatically place a landscape photo on a tall canvas, or extend the background. For a finished poster, check that it was designed for a phone screen rather than relying on a crop to convert a dense printed flyer into a usable Story.