Revert to Mountain lion from Yosemite
I upgraded and all my photo files are now in one folder and I lost the shatter effect included in iPhoto which I used a lot
You can still use iPhoto. iPhoto was not deleted from your hard drive, only removed from the Dock. If you have iPhoto 9.6.1 you can still use your iPhoto library.
If you don't have that version but some earlier version of 9.x try following Terence Devlin's instructions in this post to obtain iPhoto 9.6.1 from the App Store:
Apr 14, 2015 11:21 AM
Re: Is Iphoto gone ? i want it back!
Recommended
Go to the App Store and check out the Purchases List. If iPhoto is there then it will be v9.6.1
If it is there, then drag your existing iPhoto app (not the library, just the app) to the trash.
Install the App from the App Store.
Sometimes iPhoto is not visible on the Purchases List. it may be hidden. See this article for details on how to unhide it.
http://support.apple.com/kb/HT4928
One question often asked: Will I lose my Photos if I reinstall?
iPhoto the application and the iPhoto Library are two different parts of the iPhoto programme. So, reinstalling the app should not affect the Library. BUT you should always have a back up before doing this kind of work. Always.