Web-based services designed for human users are being abused by computer programs (bots). This real-world issue has recently generated a new research area called Human Interactive Proofs (HIP), whose goal is to defend services from malicious attacks by differentiating bots from human users. During the past few years, while more than a dozen HIP systems have been developed, there is little user study been done in evaluating HIP’s ease of use and friendliness. In this paper, we first introduce a new HIP based on human face detection, and then report a comparative user study between this new face HIP and a more conventional character-based HIP. Study results show that the users are almost equally divided in evaluating their overall ease of use.