Changing program input source from Webcam to Picturebox

hi professionals,

i have been download an open source program about face detection and it is very good and useful for beginners. i am in writing a sample face detection program and find this open source c# very good. but my problem:

in this program faces will detected from laptop webcam camera but i want to detecting faces from a picturebox (image) which i  add to the form.

i found a peace of code which i think it is about connecting to webcam camera:

private void button1_Click(object sender, EventArgs e)
        {
            //Initialize the capture device
            grabber = new Capture();
            grabber.QueryFrame();
            //Initialize the FrameGraber event
            Application.Idle += new EventHandler(FrameGrabber);
            button1.Enabled = false;
        }

so i want to change this code to sth which help me detecting from images of a picturebox in form.

thanks in your reply

and original source download link (if needed):http://199.91.152.171/xq7b5td683eg/q1g00owxbcaxyow/FaceRecProOV.rar