Získáváte duplikát, protože v albu je více fotografií. Chcete-li jej získat, použijte row_number()
:
SELECT Album_Name AS Album_Name, a.Album_Date AS Album_Date, a.Page_ID AS PageID,
p.Image_ID AS Image_ID, p.Image_Small AS Image_Small
FROM Album_Name a left outer JOIN
(select p.*, row_number() over (partition by Album_Id order by Image_ID) as seqnum
from Album_Photos p
) p
ON a.Album_ID = p.Album_ID and seqnum = 1;