I don't think that you can. I hope I'm wrong but I even had a quick google and it appears you can't disable it from what I've read. It's a shame because a lot of people find the face recognition really problematic.
Faces is now becoming a problem for me. There doesn't seem to be any way to turn off this unwanted and useless "feature" without hacking the iPhoto database files. What kind of idiot makes a resource-sucking function that can't be turned off?
I have some landscape photos right now that iPhoto is insisting contain Faces that I need to label. Go away!This software is literally crashing my Mac, freezing up and Unexpectedly Quitting, and all because this Faces junk is sucking up all the CPU and RAM. Leave Faces to Facebook, and let me import my temporary files and run my slideshow! This new iPhoto software feels like I'm running on a 400 MHz G4 with 32 MB RAM. If it can't tell the difference between inanimate objects in a landscape and a person's smiling face, what exactly is it doing with all the system resources?
faces really sucks! and iphoto needs be more simple... I dont install it, I hate it, I prefer organize my pics in simple folders with good names... I use a better finder rename, an app for rename files...
keep it simple!
(just my opinion)
I just tried: (in iPhoto 11 9.4.3 on OSX10.4.8, after having already imported some photos and so I had faces waiting to be identified)
Exit iPhoto
Open Terminal, cd to iPhoto's database directory (which on my machine is under Pictrues/iPhoto Library.photolibrary/, but that might be different on your system.):
> cd Pictures/iPhoto Library.photolibrary/Database/apdb
Disable read and write on the Faces database:
> chmod -w Faces.db
> chmod -r Faces.db
Disable read and write on the directory where Faces keeps thumbnails:
> cd ../Faces
> chmod -r *
> chmod -w *
When I opened iPhoto again, it has a "getting started with Faces" page if you click on the Faces tab. The wheel spins briefly if I import photos, but does not lock the system. No new Files are created in Faces, and time-stamp on Faces.db does not change.
I'll post again if I find that this solution has problems!
b