Canon EOS 6D Instruction Manual page 266

K Protecting Images
3 Protecting All Images in a Folder or on a Card
You can protect all the images in a folder or on a card at one time.
If you format the card (p.53), the protected images will also be erased.
Movies can also be protected.
Once an image is protected, it cannot be erased by the camera's erase
function. To erase a protected image, you must first cancel the
protection.
If you erase all the images (p.268), only the protected images will
remain. This is convenient when you want to erase unnecessary images
all at once.
266
When you select [All images in folder]
or [All images on card] in [x1:
Protect images], all the images in the
folder or on the card will be protected.
To cancel the image protection, select
[Unprotect all images in folder] or
[Unprotect all images on card].