Private Sub Timer1_Timer()
 Set Image1.Picture = Pic1.Picture(pdEMF, bAlpha)
 Set Image2.Picture = Pic2.Picture(pdEMF, 255 - bAlpha)

 Dim Alpha As Integer
 Alpha = CntI(bAlpha) + DAlpha * SAlpha
 If Alpha > 255 Then
    If bAlpha = 255 Then
       bAlpha = 255 - DAlpha
       SAlpha = -1
    Else
       bAlpha = 255
    End If
 ElseIf Alpha < 0 Then
    If bAlpha = 0 Then
       bAlpha = DAlpha
       SAlpha = 1
    Else
       bAlpha = 0
    End If
 Else
    bAlpha = Alpha
 End If
End Sub

CntI(bAlpha)

DrawBuffer = 1048576

Option Explicit

Private WithEvents Timer1 As VBAProject.Timer
Private Pic1 As CDrawingSurface
Private Pic2 As CDrawingSurface
Private bAlpha As Integer
Private DAlpha As Integer
Private SHAG_1 As String
Private SDVIG_1 As String

Private Sub UserForm_Initialize()
 Set Pic1 = New CDrawingSurface
 Pic1.LoadPicture LoadPicture(ActiveWorkbook.Path & "\Boy&Horse.jpg")
 bAlpha = 255
 Set Image1.Picture = Pic1.Picture(pdEMF, bAlpha)
 TextBox1.Value = bAlpha
End Sub

Private Sub UserForm_Terminate()
 DeleteTimer1
End Sub

Private Sub Timer1_Timer()

Set Image1.Picture = Pic1.Picture(pdEMF, bAlpha)
Set Image2.Picture = Pic2.Picture(pdEMF, DAlpha)

If bAlpha >= SHAG_1 Then
bAlpha = bAlpha - SHAG_1
Else
bAlpha = 0
End If

If bAlpha < SDVIG_1 Then
If DAlpha <= 255 - SHAG_1 Then
DAlpha = DAlpha + SHAG_1
Else
DAlpha = 255
DeleteTimer1
End If
End If

TextBox1.Value = bAlpha
TextBox2.Value = DAlpha

End Sub
Private Sub CommandButton1_Click()
 Set Pic1 = New CDrawingSurface
 Pic1.LoadPicture LoadPicture(ActiveWorkbook.Path & "\Boy&Horse.jpg")
 Set Pic2 = New CDrawingSurface
 Pic2.LoadPicture LoadPicture(ActiveWorkbook.Path & "\Chateau.jpg")
' задаем прозрачность для Pic1
 bAlpha = 255
 ' задаем прозрачность для Pic2
 DAlpha = 0
  ' задаем шаг изменения прозрачности
 SHAG_1 = 30
' задаем границу прозрачности при которой еще
'не прекратилось "стирание" первой картинки,
'но уже началось проявление второй
 SDVIG_1 = 125

DrawBuffer = 1048576

 DeleteTimer1
 Set Timer1 = New VBAProject.Timer
 Timer1.Interval = 1
 Timer1.Enabled = True
End Sub

Private Sub DeleteTimer1()
  If Not Timer1 Is Nothing Then
    Timer1.Enabled = False
    Set Timer1 = Nothing
    DoEvents
 End If
End Sub