Exactly, but they used to approach you and ask if you wanted your pic taken. I remember constantly getting bombarded every time I entered a park and realized this year that they don't do that anymore.
That was when Kodak was in the parks. Every photographer you see now is a Disney Cast Member and not a 3rd party vendor (like the balloons). A photographer may greet you, may ask you if you need help, may ask to take a picture with your camera. They are not supposed to ask you "Can I take your picture?" Although they may ask you "Do you know about the photopass service?"
Each position that a photographer is shooting from can be a "green" or "yellow" location. Green means, that position must be up at all times. Yellow means, if they're short staffed, that position may come down. As the department gets bigger, more yellows are turned into green, and more yellows are created.
Now there are certain positions that are green in the morning, but come down after the parade. Like the first three spots along Main St (Confectionery, Cinema, and Market House). And again, there's usually spots that go up in the evenings and not always during the day. Like Fantasy Land bridge (back by Cosmic Rays). Places like Castle Hub, next to Walt and Mickey will be up from 8am till park closing.
If you see a photographer wondering around Adventureland, by the tikis that squirt water. This photographer is taking pictures of Aladdin and Jasmine, but they're not out at that moment. So the photographer is filling in some time. It's a rare moment to just grab a shot of the kids playing.
If it's pouring down rain. Green location photographers will move to a rain location. Yellow location photographers will move indoors to take "fun" shots or be sent to the view stations. So you'll often times see an overload of photographers willing to show you pictures. At the same time, many people go into the shops to seek shelter, and bypass the time viewing their photos.
Castle Hub photographers will move to Tomorrowland Noodle Terrace, Casey's corner will stand under the roof by the baseball player statue. Both will continue to take photos of the castle. But most the main street photographers (wearing knickers) will move indoors. Pooh characters are sent to Expo Hall, so photographers in knickers are needed for that (their normal photographers are toontown based). Some one is sometimes sent to the Barber Shop to take pictures in there.
It's all about knowing where to look and when to look. 90% of the time, you will find a photographer with a character. Although not all characters have high enough priority to warrant a photographer with their presence. And sometimes, because of stupid rules, they can not take a picture with a certain character. Like for a while, we weren't allowed to take pictures of Buzz at the COP because he didn't have a "Pixar approved background", but you'll always find a photographer at Toy Story Mania, because that is approved. Sometimes there's clauses and royalties for taking pictures with certain characters. I think Mary Poppins is one of those.
So that's how you find a photographer.