A panorama is a 360° image. We have panorama support in the Mapillary viewer (use your mouse to pan around).
For an image to function as a panorama on Mapillary, it must be equirectangular (2:1 aspect ratio) or contain GPano Photo Sphere Metadata.
If the resolution doesn't correspond to a full 360x180 panorama, Mapillary will treat this like all other images. With some cameras, it's just a matter of a few pixels and you might be able to fix it by adding some padding to the images before you upload.
The Mapillary mobile apps don't capture stitched panoramas. You can still get a panoramic view by just capturing a sequence of photos with lots of overlap. Once uploaded, you can use navigation arrows to "look around" with smooth transitions that enable a nice 360° view of the surrounding, even though the images have not been actually stitched together.