Sub ddd()
Dim rng As Range, cell As Range, i As Long
Set rng = Application.InputBox("Выдели ячейки из которых нужно получить текст, результат будет выведен справа от каждой ячеке", Type:=8)
For Each cell In rng
txt = ""
    If IsNumeric(cell) Then
        For i = 1 To cell
            If txt = "" Then
                txt = "image_" & i & ".jpg"
            Else
                txt = txt & ",image_" & i & ".jpg"
            End If
        Next i
    End If
    cell.Offset(0, 1) = txt
Next cell
End Sub

=ЕСЛИ(A2=1;"image_1.jpg";B1&",image_"&A2&".jpg")