Web applications increasingly utilize search techniques that heavily rely on content-based text and image analyses. For example, for parental site filtering, it is necessary to identify adult sites. These applications must rely on a semantic analysis of images in the process of identification where text analysis alone is insufficient. In this article, we describe our site filtering system "WebGuard" and show the importance of image analysis in such system. Our results show that it can detect and filter adult content effectively. KEYWORDS Web filtering, Data-mining, Image analysis, Skin color model, Text mining, Semantic web