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pictureBox1.BackgroundImage = m_Image;                    

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pictureBox1.Image = m_Image;                    

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transparentePB.BackColor = Color.Transparent;
            transparentePB.Parent = mainPB;                    

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            Image i = new Bitmap(this.transparentePB.Width, this.transparentePB.Height);

            Graphics g = Graphics.FromImage(i);

            g.DrawPie(new Pen(Color.Red), new Rectangle(0,0, this.transparentePB.Width - 5, this.transparentePB.Height - 5), 0,360);

            this.transparentePB.Image = i;                    

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        Random r = new Random();

        private delegate void DrawImageDelegate(Color c);

void t_Tick(object sender, EventArgs e)
        {
            this.BeginInvoke(
                new DrawImageDelegate(DrawImage),
                Color.FromArgb(r.Next(0, 255), r.Next(0, 255), r.Next(0, 255)));
        }

        private void DrawImage(Color c)
        {
            Image i = new Bitmap(this.mainPB.Width, this.mainPB.Height);

            Graphics g = Graphics.FromImage(i);

            g.FillRectangle(new SolidBrush(c), new Rectangle(0,0, i.Width, i.Height));

            this.mainPB.Image = i;
            this.mainPB.Refresh();
        }