claim about image sha256 not true from docker v1.12

[woltere]

1.我的运行场景:

2.我的需求的具体情况（feature request || bug）:

3.重现该问题的步骤:
1.
2.
3.

4.描述您获得的实际情况:

The README.md states:

When the Docker image is pushed to Registry, a hash will be generated but the value will not change with image content. We calculate SHA256 hash of the tar file content saved with docker save, which only represents the certain image.

I think this statement is not true anymore for docker version from 1.12.

Since docker v1.12 the sha256 returned is the sha256 sum over the configuration object which contains the sha256 sums of each layer.
Layers are validated with downloaded.

5.描述您预期的情况:

Only the sha256 digest of the images needs to be linked to the image tag on the block chain.
Further more only a sha256 digest over the image digest and the address and the image tag need to be stored on the block chain.
If a verifier then wants to verify if the image is ok he can take the publisher address, image tag and the image digest and calculate the sha256 over that and look on the blockchain if it exists.

6.您认为的其他有价值的信息:

[allencloud]

ping @Revolution1 @jjyr @hainesc