Graphics

g.FillRectangle(Brushes.White, New Rectangle(0, 0, 512, 512))
g.DrawImage(Img, 0, 0, 512, 512)

Dim objImage As Drawing.Bitmap = Drawing.Image.FromFile("png_with_transparent_bg.png")
Dim booTransparentColorFound As Boolean = False
If Bitmap.IsAlphaPixelFormat(objImage.PixelFormat) Then
  For y As Integer = 0 To objImage.Height - 1
    If booTransparentColorFound Then Exit For
    For x As Integer = 0 To objImage.Width - 1
      Dim objColor As Drawing.Color = objImage.GetPixel(x, y)
      If objColor.A = Color.Transparent.A And _
         objColor.R = Color.Transparent.R And _
         objColor.G = Color.Transparent.G And _
         objColor.B = Color.Transparent.B _
      Then
        booTransparentColorFound = True
        Exit For
      End If
    Next
  Next
End If