One-Way Sync on Windows

I have pictures scattered and duplicated across multiple Windows machines. I want them all on one machine. So if picture [A,B,C] is on machine 1 and [B,C,D] is on the central server, I only want to copy A over. Pretty simple.

I tried to use unison, a fancy synchronization tool that sort of runs on multiple platforms. But I could not figure out how to get it to do this. I tried using “-force”, but it kept synching in both directions. Finally I switched to Windows’ robocopy. The command line is “robocopy /s /xc /xn /xo source-path destination-path”. The first option “/s” says to go down all directories. The other options say don’t copy the file over if the file changed or is older/newer. It’s not a clean way to do it, but it seems to work.