You can crop photos tighter or wider to include a full horizontal picture.
When you add a photo, you'll see the cropping function. You can use your cursor to select any corner of the photo to resize the crop. You can also click the three options below the photos to crop or flip the photo.
If you've already added a photo to a card, click on the pencil icon in the upper right corner of the card to get to the same cropping function pictured above.
Then, select Adjust Photo: