The official Unity Technologies de-lighting tool has been out for quite some time now for photogrammetric assets. If you are a complete starter, you can find a technical walkthrough on how to best approach photogrammetry here from Unity,
Today we're just going to talk about the de-lighting package you can use to remove dynamic lighting from any object from within Unity after you've photo-generated your 3D assets. You'll then be able to use these assets in any environment.
At the moment, the package does not work in any version of Unity 2018.x so you'll have to do any processing in the 2017 version.
Much to my delight, I have recently stumbled upon a means of turning any 3D asset into a 2D sprite or collection of sprites from within Unity. I could take any model, with a de-light material - still ripe with texture information - and render it to out to a single sprite or a sequence of sprites.
The image below is a 100 x 100 pixel image of a sprite that was taken of the model directly from Unity. You can attach animations to models and render out deformation, reorientation, etc. to get any sort of flipbook animation (at any image size that you might want!)