As the detection key in symmetric watermarking scheme can be used to forge or remove watermarks from digital works, it is required that the detection key be secret in watermark detection procedures. Based on zero-knowledge and proof of knowledge concepts and protocols in Cryptology, zero-knowledge watermark detection protocols can make the verifier believe the presence of a watermark in a disputed digital work while not compromising the detection key. The security requirements of a publicly verifiable zero-knowledge watermark detection scheme are outlined in this paper. Then a publicly verifiable commitment scheme and a zero-knowledge proof of knowledge protocol which proves knowing the discrete logarithm of a committed value are presented. Finally, using the above scheme and protocol as building blocks, a publicly verifiable zero-knowledge watermark detection protocol is proposed and its security considerations are addressed.