A method and system for detecting and preventing fraudulent health care claims. A bar code having a service date and provider ID is generated. The provider ID identifies a health care service provider that is requested to provide a service to a client on the service date. A digital image file that includes the bar code, transaction data, and a signature is received. The signature, transaction data, provider ID and service date are extracted from the digital image file. Verification software determines whether the extracted signature matches the client's reference signature stored in a database. Verification software determines whether extracted data that includes service date, provider ID, and client ID is included in any transaction record in the database. A report is generated that identifies a fraudulent claim if the extracted signature does not match any reference signature or if the extracted data is not included in any transaction record.