Image signing is a way to attach cryptographic proof to a container image so others can verify where it came from and whether it was changed. A signer creates a digital signature over the image or its digest, and a verifier checks that signature before pull or deployment.
This matters because registry authentication only proves who can upload an image, not whether the image is trustworthy after upload. In attacks, an adversary who gains registry access or tampers with a repository may try to replace a legitimate image with a malicious one under the same tag. Signing helps defenders detect that mismatch, especially when combined with digest pinning and policy checks in CI/CD or admission control. Used correctly, image signing turns container trust from “who pushed this” into “can this exact artifact be proven authentic.”