The printing GraphicsUnit is Display, which is 1/100th inch, while the image unit is Pixel. Convert the image measurements to Display units, then you can do the logic math with comparable values. Example:
Code:
Dim img As Image = Image.FromFile("img.bmp")
'image size in 1/100 inch measurement
Dim sz As New SizeF(100 * img.Width / img.HorizontalResolution, _
100 * img.Height / img.VerticalResolution)
Dim p As New PointF((e.PageBounds.Width - sz.Width) / 2, _
(e.PageBounds.Height - sz.Height) / 2)
e.Graphics.DrawImage(img, p)
img.Dispose()