The world and events that happen around us don't really exist anywhere but in our minds. We don't know something exists until we have experienced it. And our minds don't do the best job of containing the intangible information of life and the world around us.
Photographs take things that exist and put them right in front of us.
For example, how many people would have known about the tsunami without the aid of the media? There are some people who didn't even know how to pronounce the word tsunami let alone know what one was.
Another example. If I say Moscow, London, Paris, Egypt, Las Vegas or Antarctica. Pretty much all of us can conjur up an image of what that place looks like (or at least parts of that place), even though we may never have been there. And that is thanks to images.