Canon MARK IV User Manual (en)

Custom Function Settings
C.Fn IV -15     Add aspect ratio information
During Live View and movie shooting, vertical lines corresponding to the 
aspect ratio will be displayed. You can thereby simulate still photo framing 
for medium- and large-format film sizes such as 6x6 cm, 6x4.5 cm, and 4x5 
This aspect ratio information will be appended automatically to the captured 
image. (The image will not be saved to the card as a cropped image.)
When the image is transferred to a personal computer and Digital Photo 
Professional (provided software) is used, the image will be displayed in the 
aspect ratio you specified.
0: Off
4: Aspect ratio 6:7
1: Aspect ratio 6:6
5: Aspect ratio 10:12
2: Aspect ratio 3:4
6: Aspect ratio 5:7
3: Aspect ratio 4:5
C.Fn IV -16     Add image verification data
0: Disable
1: Enable
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.157), the <L> icon 
will appear.
To verify whether the image is original, the Original Data Security Kit 
OSK-E3 (sold separately) is required.
Aspect ratio information will also be appended during viewfinder 
During image playback on the camera, vertical lines for the respective 
ratio will be displayed.