My photobooth is gone, and its not in the installer disks. How do I get it back?

I noticed this morning there was a question mark on my photobooth icon in the dock. Saw I go to click it, and nothing would happen. So i decided to go on the applications folder and open photobooth. But it wasnt THERE EITHER! So i go to the Install Disk 1, and i go to optional downloads, and its still not there. So i go to download all applications, and once it was done, it still wastn there. Its really sad, because it was my favorite app. Hope you guys can help.