using System.Drawing.Drawing2D;
private void button3_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
  { this.button3.Cursor = Cursors.Hand;
         Bitmap bmpBob =(Bitmap)this.button3.Image;      
      GraphicsPath graphicsPath = CalculateControlGraphicsPath(bmpBob);
     this.button3.Region = new Region(graphicsPath);  
  }
  private static GraphicsPath CalculateControlGraphicsPath(Bitmap bitmap)
  {
  
   GraphicsPath graphicsPath = new GraphicsPath();  

   Color colorTransparent = bitmap.GetPixel(0, 0);
  
   int colOpaquePixel = 0;
  
   for(int row = 0; row < bitmap.Height; row   )
   {    
    colOpaquePixel = 0;
  
    for(int col = 0; col < bitmap.Width; col   )
    {
    
     if(bitmap.GetPixel(col, row) != colorTransparent)
     {
      
      colOpaquePixel = col;
    
      int colNext = col;
    
      for(colNext=colOpaquePixel; colNext<bitmap.Width; colNext  )
       if(bitmap.GetPixel(colNext, row) == colorTransparent)
        break;
    
      graphicsPath.AddRectangle(new Rectangle(colOpaquePixel,
       row, colNext - colOpaquePixel, 1));
    
      col = colNext;
     }
    }
   }  
   return graphicsPath;
  }