The photographs are everywhere! They will find you when you are boarding the ship, at dinner, at deck parties, when you get off in the ports of call, in the evening before dinner. You can pass up the opportunity for a photo any time, but there are no fees for them to take your pictures. The only time you are charged is if you purchase the photos. Some of the photos will be connected with your key card on some ships. On others, you will just go to the photoshop area and view the photos taken. These are generally organized by when they were taken.
A word of caution for some cruises. When we got onboard for our Norwegian cruise, they used a green screen for a backdrop. This allowed them to put a picture of the ship behind us or other backgrounds. They used the same photo for a few different backgrounds. We only had to get one picture taken, but we had multiple pictures to choose from. If you are wearing a green shirt, your photo will be distorted. We are Green Bay Packer fans and my husband wore a green Packer shirt when we were embarking. As a result, he had a ship sailing through his tummy in the pictures!
Most lines will have a package deal if you want to purchase more than one photo over the course of the cruise. Check these out as it can save you a lot of money over the course of the cruise. You'll also want to be aware that if you find a photo of yourself and you really want to get it, you should do so soon. The pictures do get moved and consolidated. They only have so much room to display them. This is especially a concern on longer cruises. As I mentioned before, this is a great way to get a nice family portrait!