The excerpt post style has an option of showing 2 featured image in horizontal and vertical position. By default if a post only have one featured image, it will show the same image both for horizontal and vertical version.
Alternatively, you can change this setting from Appearance >> Customize >> Post Settings. Under “How do you want excerpt style posts to look like when there is only one featured image?”, you can either choose:
- Show the same featured image twice for both landscape and portrait positions (default), or
- Show the featured image once in landscape position, or
- Show the featured image once in portrait position
How to upload a second featured image
Featured image boxes are located on your post editor.
The main featured image is the one in horizontal position and is uploaded to the Featured Image box as shown below. The second featured image is the one in vertical position and is uploaded to Second Featured Image box as shown below.