If the GPS is mostly off (i.e. you're only rarely using your GPS app), I think you will get ~2 days of battery life. To get that much battery life, you'd need to do these things:
- Keep the GPS off as much as possible (i.e. use it no more that 5-6 times a day)
- Turn it off at night completely
- keep brightness to a minimum
- Disable all cellular antennas (may need to jailbreak to do this)
- remove unnecessary apps, especially anything that wants to run in the background
- turn it off during the day as much as possible
So even with all that, you're looking at 2 days.
What can you do beyond that? I think the simplest solution to get you the recharge you'd need is to buy an iPhone battery case - usually this is just an external Li-ion battery that plugs into your iPhone. These are pretty common, fairly light, and generally easy to use. They also have the advantage of often combining in a waterproof case (so you can take pictures even if it is raining). The limitation might be that it doesn't actually get you enough charges for what you want to do (a bazillion pictures are a lot!)
I agree that hand-cranks and solar chargers are not nearly reliable enough.
So the only other solution that I might consider is something that eats AA Li-ion disposable batteries (or if you feel environmentally friendly, the best AA rechargeables you can find) and spits out power via USB. Tekkeon makes a couple products that might be the right kind of thing (I've used one before that worked perfectly)... You might try this one. Li-ion AAs are very light, although expensive, and each set of 2 will charge your iPhone 1-2 times (depends on which AA charger you get and which iPhone you have... might be best to test this before you leave!).