Spherium searches your iOS library for 360º degree equirectangular images.
What is a 360 Photo
Normal photos capture what is in front of the camera. 360º photos capture what is all around the camera in every direction.
What is Equirectangular Projection
The wikipedia article on it has more information, but effectively a equirectangular projection is a way of stretching the pixels from a sphere into a flat 2:1 image.
Spherium looks for images which are exactly 2:1 (w:h) to indicate they might be a 360º photo.
How Do I Take a 360 Photo
You typically use a dedicated 360 camera, which captures 2 images from fisheye lens at slightly more than 180 degrees and then merges the two images into one 360 image.
However, there are also apps that can stitch together a 360º panorama on device from a series of photos in different directions; and several drones have a 360 panorama capture mode.
How Do I View 360 Photos
Spherium automatically shows you all the 360 photos in your iOS Photo Library and allows you to view them on your iPhone or iPad.