If your Plone site uses Postgres it is very likely using RelStorage. Please check the documentation for Relstorage, you can configure it to store both (meta)data and blobs all in the postgresql database, but there is also a setting to store the blobs (images/files) in a separate filesystem blobstorage.
If your restored postgres db misses files an images, it's very likey they were stored in the docker container. Maybe you need to add an extra volume/bind mount to a specific path in the container to store these.
( Or you need to pass different options to the container to instruct RelStorage to store all data in Postgres, but that won't help you much in the current situation. Once you have your database and blobs 're'-synced, RelStorage has a zodbconvert script that could help you convert postgres/filesystemblobs to postgres only)