The ashy effect used in Avengers: Infinity War is quite easy to recreate in Photoshop. You take a photo, copy some layers, and liquefy/warp one layer. Then you create your own brush in Photoshop and use it on both layers, one to make the body of the subject look like its disintegrating, one to make it look like the ashes are blowing away. This isnt the best explanation, but there are many sites where you can find a more in-depth description.