It's been a while since I did the precise task of remapping textures to an object, but here are lots of ways to go about it. It's particularly easy if your photos are guaranteed to cover the entire sphere. A quick search for "create 3d model from photos" should off insights for that as well as suggestion for automated or semi-automated processes.

One way to do manual alignment is to use a 3D program like Blender and align your photos as textures over a sphere ( https://blender.stackexchange.com/qu...ge-on-a-sphere ). Bake the aligned textures into a single spherical UV map for the sphere and there's your Equirectangular map. More images with overlap is better, of course, but you can do this with just a few images if needed (or half of a sphere from just one image as they did with early moon mapping as described at https://www.futurity.org/moon-maps-l...nding-2109642/ ).

Another good search term is for "create 360 panorama from photos". Looking from the center of the sphere outwards (a panorama) is more or less the same problem as looking at the center of a sphere.