The easiest way to make this customization is using Deeper. Just choose your logo and the app will do the rest!
If you like to take the manual approach, the instructions are the same as found on OS X Daily, but I found that making sure the image file was exactly 428 x 248 pixels and in a .png. You can download the Starfleet emblem that I used below:
You need four copies of this file, and they need to be named:
I don’t know why these are like this, but it works! Once they are named correctly, just drag them into the following path:
and then choose to replace all of them.
Log out and you should see your custom logo at the login window!
To add even more customization, change the picture associated with your user!
See original blog post at http://jacobsalmela.com/os-x-mavericks-change-login-window-logo-wallpaper/?utm_source=rss