The image can be built from source by running:
docker build .
A recommended security practice is to add an additional unprivileged user to run the daemon as on the host. For example, as a privileged user, run this on the host:
useradd bitcoind
To build an image which uses this unprivileged user's id and group id, run:
docker build --build-arg USER_ID=$( id -u bitcoind ) --build-arg GROUP_ID=$( id -g bitcoind ) .
Now, when the container is run with the default options, the bitcoind process will only have the privileges of the bitcoind user on the host machine. This is especially important for a process such as bitcoind which runs as a network service exposed to the internet.