even failed builds make images, of course

output.txt

$ docker build --rm -
FROM busybox
RUN true
RUN true
RUN true
RUN false
<Ctrl+D>
Uploading context 2.048 kB
Uploading context 
Step 0 : FROM busybox
 ---> 769b9341d937
Step 1 : RUN true
 ---> Running in f7af33b73c4d
 ---> fcbd472e722b
Step 2 : RUN true
 ---> Running in b0417cf74d15
 ---> adea7119af9b
Step 3 : RUN true
 ---> Running in f2fd3d9cfb45
 ---> 937771dc045a
Step 4 : RUN false
 ---> Running in b811e52ed076
2014/02/28 09:25:35 build: The command [/bin/sh -c false] returned a non-zero code: 1
$ docker images | grep 937771dc045a
<none>                    <none>                                                        937771dc045a        25 seconds ago      2.489 MB