This paper used the bibliometric analysis to identify the productive countries generating internationally co-authored articles on watermarking, based on articles published between 1991 and 2012. The main research focus is the trend in the scientific collaboration strengths between productive countries. The findings showed a slightly increasing trend was observed in the annual proportion of international co-authored articles after 1995. The U.S. is the most productive country generating internationally co-authored articles. Among top 10 productive countries, the pair of U.S. and Italy had the largest value of the scientific collaboration strength. However, no increasing trends appeared in the scientific collaboration strength between them.