Reinstall damaged iPhoto without disc
I recently got a Macbook Pro Mid-2012 with OSX 10.8.3 which owned by my brother previously. However the iPhoto can not be opened and always says that it is damaged. I tried to look for any solution, but nothing worked.
1. Some said that I can reinstall it through DVD which come with Macbook. Unfortunately, this Macbook doesn't have any DVD inside the package.
2. I also tried to open the Recovery mode. The only option I found here is only to reinstall the OS completely.
3. Then I went to App Store, looked for iPhoto in my (and my brother's) Purchases tab. Still, I could not find iPhoto.
Is there any option for me to get back my iPhoto? I know iPhoto is a bundled apps comes with every Macbook and I don't want to spend $15 buying something I already have.
Thanks.
MacBook Pro (13-inch, Mid 2012), OS X Mountain Lion (10.8.3)