<p>Current optical image watermarking schemes generally embed watermark information by modifying the host image, making them unsuitable for applications that require high integrity of the host image. Furthermore, the existing biometric-based optical image watermarking schemes rely on the single modal biometric keys, which falls short of meeting the high-security demands of optical information security systems. To address these issues, this paper proposes an optical robust zero-watermarking scheme based on phase-truncated fractional random transform and multimodal biometric keys. In this proposed scheme, a pseudo-noise-like watermark image is generated using the random phase masks constructed from both the human face and fingerprint biometrics, in combination with the phase-truncated fractional random transform. XOR, the encoded watermark with the texture features of the host image to obtain the zero-watermark image. During copyright verification, only when both the human face and fingerprint inputs are correct the original watermark information be used successfully decoded. Additionally, since the host image remains unaltered, this proposed zero-watermarking scheme is suitable for scenarios where image integrity is critical. Extensive experiments demonstrate that this proposed scheme not only offers high security but also exhibits strong robustness against image processing attacks and geometric attacks.</p>