HT1338: OS X: Updating OS X and Mac App Store appsLearn about OS X: Updating OS X and Mac App Store apps
Currently Being ModeratedAug 17, 2012 6:49 PM (in response to hodoali)
You will need to reinstall it, and that can be done from either a Time Machine Backup, or a clone of your HDD kept on an external drive, or from your ORIGINAL install disks.
This means for example if you upgraded to 10.6 from a Retail Snow Leopard DVD you won't have iPhoto on there, rather you will need to extract it from the original Install DVD.
If you need to get your iPhoto from an older DVD say, 10.5 DVD, then the best method is to extract the iPhoto app, from that DVD using the application Pacifist. downloadable from this link.
Currently Being ModeratedAug 18, 2012 8:56 AM (in response to hodoali)
If you purchased it in the app store and didn't have a disc, you should be able to sign into the app store with the same apple id and and password then go into purchases at the top and download it again