Step 2: Locate the InstallPrinter script that you just downloaded in the Finder and double-click to run the script.
You saw this box because you are running Mac OS 10.8 Mountain Lion, and you have set Gatekeeper to prevent you running unidentified programs that you download from the Internet. To override Gatekeeper and run the printer installation script, do the following:
Right-click on the InstallPrinter script, and choose Open from the pull-down menu.
Click Open in the "InstallPrinter" is from an unidentified developer... box.
Click to close.
You saw this error message because you do not have the HP Printer software, including the driver for the Library printer, installed on your Mac. To install the software, go to the Apple Support Downloads page and search for HP.
In the HewlettPackard Printer Drivers window, double-click to open the software package.
The software installer will open. Click Continue and follow the usual installation steps.
Click to close
Now locate the InstallPrinter script in the Finder, and double-click to run it again.
When the script is successful, you will see the following alert:
If you look in your Print or Print & Scan settings, you will see that the Library printer, MPL, has been installed.
You can now begin printing.
Pick up your print jobs at the Left Print Release Station using your login ID. Return to printing instructions.