js文件https://github.com/jaysalvat/jquery.facedetection

$(function () {
    $('#img').faceDetection({
        complete: function (faces) {
            if (faces.length == 0) { //说明没有检测到人脸
                alert("无人脸")
            } else {
                for (var i in faces) {
                    draw(faces[i].x, faces[i].y, faces[i].width, faces[i].height);
                }
            }
        },
        error: function (code, message) {
            alert("complete回调函数出错")
        }
    })
})