IMHO 3 days 2 night is almost ok already, not much special place there...Unless you can just stay at the 'not so attractive beach (of Langkawi main island)' for whole morning / afternoon, then maybe 4 days.
Should be better to rent a car. Price should not be more then RM100 per day. Should able get from airport.
Accommodation I have no experienced on a lot of choice, I stayed in the one near Airport (Angsana or what start with A... ;p forgot) Just don't stay at Kuah (the town) will do.
But for photo shooting, a few listed.
1. Go island hoping. A half day tour should enough. The concept something like Phuket's island hoping, but just less attractive compare to the former. Go the "Pulau Dayang Bunting" where there is a special lake (
http://www.langkawi-beaches.com/langkawi-islands.html)
2. The cable car. Must go
3. When driving to the cable car place, you will pass a 'port' that got a lot of small yacht, something like Sentosa's cove. It's called "Telaga Harbour Park" (
http://www.langkawi-info.com/pantai-kok/where-to-go.htm)
4. Mahsuri's Tomb (Mausoleum). Not very special place, but while on your way, you might found there is a few paddy field with beautiful background worth photo taking.
Check out the web link given.