Canon EOS 5D Mark II Instruction Manual page 185

C.Fn IV -6
0: Off
1: On
Data for verifying whether the image is original or not is appended to the
image automatically. When the shooting information of an image
appended with the verification data is displayed (p.129), the <L> icon
will appear.
To verify whether the image is original, the Original Data Security Kit
OSK-E3 (sold separately) is required.
The images are not compatible with the image encryption/decryption
features of Original Data Security Kit OSK-E3.
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Add original decision data
3 Custom Function SettingsN
185