G’MIC is an open-source image processing framework. While it is primarily known for GIMP, they provide a version (via the gmic_photoshop_plugin ). It contains a specific filter called “JPEG Artifacts Removal” (under Degradations -> Repair ). This is entirely free and updated regularly.

If you cannot install third-party filters (e.g., on a work computer), Adobe has a hidden gem: .

However, I can give you a – a fictional but realistic narrative about someone discovering such a tool, along with the closest legit free methods available today.