Sub TestCaption()
Const fName1 As String = "1 Dog is brown. Dog is big.jpg"
Const fName2 As String = "1.2 Cat is black. Cat is little.jpg"
Const fName3 As String = "2 Pencil is a yellow. Pencils are great.jpg"
Dim sCaption As String
    sCaption = GetCaption(fName1)
    MsgBox sCaption
    sCaption = GetCaption(fName2)
    MsgBox sCaption
    sCaption = GetCaption(fName3)
    MsgBox sCaption
End Sub

Function GetCaption(sName As String)
Dim sCaption As String
Dim iPos As Integer
    If IsNumeric(Left(sName, 1)) = True Then
        iPos = InStr(1, sName, " ")
        sCaption = Mid(sName, iPos + 1)
    Else
        sCaption = sName
    End If
    sCaption = Left(sCaption, InStrRev(sCaption, "."))
    GetCaption = sCaption
End Function