I lost my iPhoto

reinstall from the original source

Could be

1 - the restore disks that came with the computer - if it came with CDs and you do not know where they are then contact Apple to see if they can be replaced

or

2 - the iLife DVD that you purchased

or

3 - the app store - log in under the Apple id used to purchase the software or to set up the computer - look under purchases - you might have to unhide or accept the Application first

LN