To resize a picture you don't need a picturebox.
Try the follow code example:

Dim Scale As Double
Dim NewWidth As Integer

Dim p1 As New System.Drawing.Bitmap("picture.jpg")

Scale = p1.Height / p1.Width
NewWidth = 200

Dim p2 As New System.Drawing.Bitmap(p1, NewWidth, CType(NewWidth * Scale, Integer))

p2.Save("new picture.jpg")

p1.Dispose()
p2.Dispose()