VB .NET Capturar Tela

Adicione no seu form:

1 Picturebox e 1 Button.

Public Class Form1

    Inherits System.Windows.Forms.Form

    Private Declare Function CreateDC Lib "gdi32" Alias "CreateDCA" (ByVal lpDriverName As String, ByVal lpDeviceName As String, ByVal lpOutput As String, ByVal lpInitData As String) As Integer

    Private Declare Function CreateCompatibleDC Lib "GDI32" (ByVal hDC As Integer) As Integer

    Private Declare Function CreateCompatibleBitmap Lib "GDI32" (ByVal hDC As Integer, ByVal nWidth As Integer, ByVal nHeight As Integer) As Integer

    Private Declare Function GetDeviceCaps Lib "gdi32" Alias "GetDeviceCaps" (ByVal hdc As Integer, ByVal nIndex As Integer) As Integer

    Private Declare Function SelectObject Lib "GDI32" (ByVal hDC As Integer, ByVal hObject As Integer) As Integer

    Private Declare Function BitBlt Lib "GDI32" (ByVal srchDC As Integer, ByVal srcX As Integer, ByVal srcY As Integer, ByVal srcW As Integer, ByVal srcH As Integer, ByVal desthDC As Integer, ByVal destX As Integer, ByVal destY As Integer, ByVal op As Integer) As Integer

    Private Declare Function DeleteDC Lib "GDI32" (ByVal hDC As Integer) As Integer

    Private Declare Function DeleteObject Lib "GDI32" (ByVal hObj As Integer) As Integer

    Const SRCCOPY As Integer = &HCC0020

    Private oBackground As Bitmap

    Private FW, FH As Integer

    Protected Sub CaptureScreen()

        Dim hSDC, hMDC As Integer

        Dim hBMP, hBMPOld As Integer

        Dim r As Integer

        hSDC = CreateDC("DISPLAY", "", "", "")

        hMDC = CreateCompatibleDC(hSDC)

        FW = GetDeviceCaps(hSDC, 8)

        FH = GetDeviceCaps(hSDC, 10)

        hBMP = CreateCompatibleBitmap(hSDC, FW, FH)

        hBMPOld = SelectObject(hMDC, hBMP)

        r = BitBlt(hMDC, 0, 0, FW, FH, hSDC, 0, 0, 13369376)

        hBMP = SelectObject(hMDC, hBMPOld)

        r = DeleteDC(hSDC)

        r = DeleteDC(hMDC)

        oBackground = Image.FromHbitmap(New IntPtr(hBMP))

        DeleteObject(hBMP)

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        CaptureScreen()

        PictureBox1.Image = oBackground

    End Sub

End Class

Espero ter ajudado e att.