We have recently reported the photo-memory effect on boron-doped semiconducting diamond surfaces, which involves the photoelectrochemical pretreatment and subsequent sensitized deposition of copper and which we have referred to as the 'photographic diamond surface phenomenon' [S. Yoshihara, K. Shinozaki, T. Shirakashi, K. Hashimoto, D.A. Tryk, A. Fujishima, Electrochim. Acta 44 (1999) 2711]. In the present work, the origin of this phenomenon was investigated by AC impedance and contact angle methods. After polarization at -0.25 V versus SCE in aqueous H2SO4 solution under UV illumination, the surface exhibited the photographic effect. The polarized surface showed higher surface conductivity and increased hydrophilicity. Also, surface analysis suggested that the polarized surface has a higher surface coverage of hydrogen. These results strongly suggest that this phenomenon is related to changes of the surfacial functional groups induced by photoelectrochemical hydrogen evolution.