Det ser ud til, at du lider af MySQL's manglende evne til at foretage sene rækkeopslag:
Prøv dette:
SELECT p.*, u.*
FROM (
SELECT id
FROM photo
ORDER BY
uploaddate DESC, id DESC
LIMIT 10
OFFSET 100000
) pi
JOIN photo p
ON p.id = pi.id
JOIN user u
ON u.user_id = p.user_id