Recently, Onscreen Marking (OSM) system based on the traditional cloud platform has been widely used in various large-scale public examinations. However, the mainstream examination marking process is not transparent, and there is the possibility of a black-box operation, which damages the fairness of the examination. Also, the issues related to data security and privacy are still considered to be serious challenges. In this paper, we deal with the above problems by providing secure and private transactions in a distributed OSM assuming the semi-trusted examination center. We have implemented a proof-of-concept for a consortium blockchain-based OSM in a privacy-preserving and auditable manner, enabling markers to anonymously mark to the distributed ledger.