Unknowingly I have deleted the below buckets from my project
artifacts.<PROJECT-ID>.appspot.com
us.artifacts.<PROJECT-ID>.appspot.com
This has deleted all the images from gcr. Let me know if the above buckets are where the gcr images are stored or is it something else?
Also when I created a new image and pushed it to gcr, all the deleted images in gcr console got recovered. But whenever I try to pull any old image it is throwing "unknown blob" error.
Yes, these buckets are where the docker container artifacts are built and stored..(Artifacts being the build steps results, that add up to an image)
Then they are referenced by the Google Container Registry (i.e. gcr.io), but they will be still located in your bucket.
Since you removed the bucket and its contents, you will be missing old building steps from your built images, that's why you get the error pulling image configuration: unknown blob error message.
For example, I uploaded a new image following this documentation, and I removed the artifacts.<PROJECT-ID>.appspot.com bucket afterwards. Then I reuploaded it, using a tag (I used quickstart-image:tag1, and when pulling it this way:
docker pull gcr.io/wave16-joan/quickstart-image:latest
I got the error pulling image configuration: unknown blob error message, because it's missing the steps I already had in my previous build.
However, doing this:
docker pull gcr.io/wave16-joan/quickstart-image:tag1
Allowed me to pull the image, but the image wasn't usable.
Regarding your second question, I believe that the reason why you are seeing in the Container Registry references to the images you removed, it's because GCR is still saving the references to the steps from building these images, however since they are deleted, they are not able to be pulled.
