You can pull a specific image by digest by using the following syntax:
docker pull ubuntu@sha256:45b23dee08af5e43a7fea6c4cf9c25ccf269ee113168c19722f87876677c5cb2
If you need to find the hash, it is output when pushing/pulling the image. Some automated builds output it at the end. I tried looking for the hash with docker inspect but it didn’t appear to be there, so you’ll have to delete the image and pull it again to view the hash.