I've download a lot of images in one directory including
I want to split the directory into two.
I'm looking for a Linux command line tool to filter by face.
You can sorta already do this with Picasa + gData API + GoogleCL.
As you know, Picasa has facial recognition, and the Google Data web API can access this. So the last piece of the puzzle is GoogleCL, which gives you access to Google services (via gData) from the command line.
I'm not sure how easy it is to do this out of the box. Perhaps you'll be the first person to attempt to access Picasa's facial recognition data via GoogleCL and you'll need to add support for it yourself. But GoogleCL already supports at least some Picasa API functions, so it shouldn't be too hard to figure out if you have some programming experience.