Greece is a photographer's paradise!
Everywhere you turn there are subjects that would make great photos. Landscapes, historical artifacts, people, street life, animals, and sunsets will keep your eye behind your camera constantly, and will provide you with incredibly beautiful photos.
Photographing in ancient sites is permitted with a handheld camera without a flash in all museums and archaeological sites. There are certain areas where photography is restricted in museums, and they are marked by signs in many languages. You can arrange for special photographing conditions at museums and ancient sites by paying a fee and obtaining a license from the ministry of culture.
The light inside museums is low so you might want to change your camera to a higher ISO. ISO 400 seems to be adequate, even though in consumer digital cameras it leads to more, "noisy" pictures.
Also, in museums many artifacts are exhibited behind glass which makes photographing them a real challenge. A polarizing filter can help eliminate glass reflections, and it can also be useful in eliminating glare from landscape pictures. If you don't a polarizing filter, shooting at an angle to the glass can help eliminate glare.
One surprising museum policy prevents visitors from photographing ancient statues with people next to them. When I asked at several museums I received the same answer: "the rule is created out of respect for the statues". I assume the rule was put into place to prevent rowdy visitors from reacting to the nudity of the statues by posing with them in "funny" ways.
While photographing is allowed in most Greek museums, it is forbiden is some (like the Vergina tumulus/museum, and the Acropolis museum), and in some they will ask you to check-in your camera at the entrance (like in the Benaki museum in Athens).
If you know about Greece only from photographs of vivid blue skies and water, you might be surprised at how hazy the Greek horizon is. During most summer days it would be hard to distinguish the horizon line due to the high heat.
If you want to bring out the dark blue of the sky and the ocean in your photographs, you should expose for the sky. A circular polarizing filter can also be very helpful to eliminate hazy photographs, but the best technique is to shoot early in the morning within one hour of sunrise, when the light is pure and the landscapes are still crisp and colorful.
I have found that on very windy days the landscapes of Greece look very clear, and conditions are generally best for photographing during the day, and especially during sunsets.
No matter what equipment you use, you will need to recharge your batteries at least once per day. Electricity in Greece is 220V (50Hz), and it would be best to inspect your battery chargers before you travel to Greece. Most likely, your adaptors are rated to handle up to 240V, and such capabilities are usually printed on the charger itself or in the manual.
If your equipment is not rated for the Greek electrical current (220V), you need to purchase an electrical transformer (differnet from "electical adaptor"). You can find the amount of voltage your equipment can handle in the user manual, or on the label that often exists on the applience itslef.
Also, read more about what to take on your trip to Greece which includes more advice about electricity and electronics.
All the old "one hour photo" shops, even in the smallest of towns, have converted to accommodate digital processing. You can take your media to most Photo shops in Greece, and within a reasonable amount of time (usually within an hour) you can have paper prints back.
Media accepted is not limited, and they can even burn your digital images on a CD so you can format your card and keep shooting more photographs. All you have to do is to deliver your storage media to the store, go have some coffee, and come back to collect your paper photos and/or disk.
A word of caution is warranted here. Most people would unload their photos on a disk to make room for more photos. So, once they get their disk from the store they assume they can delete all the photos from their card. But think how many times you have burned a disk only to find out that the disk doesn't work for one reason or another.
To avoid losing all your photos, you may ask the photo processing shop to test the disk on their pc before you go deleting your pictures from your camera.
Film is getting more difficult to find these days in Greece. If you do use film, I would recommend buying your film before you get to Greece. If you do buy some in a Greek photo store check the expiration date, as it might be too old for shooting photographs.
If you do shoot on film, make sure you always have enough film when you visit archaeological sites because most offer no photo supplies on the grounds, and processing might be limited to specialty shops in the lagest cities only.
You can also find Mini DV tapes in almost every city in Greece.
You can buy them in just about every electronics store even in small towns. But even that is now becoming rare since most camcorders have an internal hard drive for video storage and don't rely on removable media any more.
One-hour photo stores offer a variety of accessories, but the larger selection can be found in electronics shops, especially in Athens and other large towns around Greece. Accessories can be found in small towns and islands, but the prices are much higher.
There are several shops that sell digital cameras and accessories, but the most ubiquitous one seems to be the "Germanos" chain of stores. If you need an extra battery, or extra media for your camera or camcorder chances are you will find it at Germanos, and you can find a "Germanos" shop in every town in Greece.
The prices of electronics in Greece are high, so it would be wise to plan ahead and to use such shops only in an emergency.
Being in Greece means that inevitably you will be around water, salt water, or fine sand, for much of the time. Make sure to pack some large Ziploc bags to keep your equipment dry during freak thunderstorms, and when you get drenched on a boat bouncing over the choppy waves.
Paradoxically, ziploc bags are almost impossible to find in Greece, so I have learned to take with me an entire box to make sure that my electronic equipment will stay dry and sand-free. They are also a great way to pack cables and electronics in your luggage, or to store your wet bathing suit in your backpack, so such clear bags have multiple uses.
With a little bit of planning you can preserve precious memories that are sure to make you long for returning to Greece again.