If you have migrated from Linux to OSX… you might well be missing ssh-copy-id. Frankly, the easier way to do this is to install the Brew repository / package manager for Mac and then install ssh-copy-id on your Mac in one command.
Install Brew (if you don’t already have this awesome tool!).
ruby -e "$(curl -fsSL https://raw.github.com/Homebrew/homebrew/go/install)"
brew install ssh-copy-id