Questo l'ho appena provato e funziona correttamente
codice:
Private Sub PictureBox1_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PictureBox1.MouseDown
        PictureBox1.DoDragDrop(PictureBox1.Image, DragDropEffects.All)
    End Sub

    Private Sub PictureBox2_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles PictureBox2.DragDrop
        PictureBox2.Image = e.Data.GetData(DataFormats.Bitmap)
    End Sub
    

    Private Sub PictureBox2_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles PictureBox2.DragEnter
        e.Effect = DragDropEffects.Copy
End Sub