Complete the final mission in the QR Code Investigation
Difficulty (Medium/Hard)
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This can still be done in free roam after beating the story.

There are a total 16 QR Codes. You have to find them all to unlock a mission. Completing this mission will then unlock the achievement.
To complete a QR Code you must find one specific surveillance camera and look at the Code from a certain angle. The correct camera is sometimes far away, or can only be activated from an elevated position.