imports System.Drawing.Drawing2D
.
.
Dim c1 as Color = Color.FromArgb(0,0,0)
Dim c2 as Color = Color.FromArgb(255,255,255)
Dim rc as new Rectangle(0, 0, Me.PictureBox1.Width, Me.PictureBox1.Height)
Dim b as new LinearGradientBrush(rc,c1, c2, LinearGradientMode.Vertical)
Dim g as Graphics =Me.PictureBox1.CreateGraphics()
g.FillRectangle(b, rc)
g.Dispose()