If it only writes zeros and nothing else, the images are still easily recoverable. Jpgs can easily be recovered even after the whole disk had been filled (with files/normal data), formatted and repartitioned several times.
Can you provide some evidence or a link to someone who has actually done this?
From everything I've read, the commercial data recovery companies say that recovery is impossible even after a single wipe with 0's.
The one I recommend definitely works on a card that is formatted in camera, formatted hard drive on pc etc..
do these softwares work if the cf card has been re formatted in the camera or only if they have been deleted?
It depends on the type of format you do in camera. The 6D provides an option of a "low level format" of a SD Card which writes zero values to the memory. The images are no longer recoverable in such a case.
If it only writes zeros and nothing else, the images are still easily recoverable. Jpgs can easily be recovered even after the whole disk had been filled (with files/normal data), formatted and repartitioned several times. It is possible to make the jpgs unrecoverable even if you deleted them normally without overwriting them but it's more tedious to do it afterwards. It is generally easier to recover images than it is to make them unrecoverable. You can recover most jpgs easily with the unix program recoverjpeg.
No you cannot. Try it.
I'm not a scientist so you're better off looking for the information elsewhere, but first of all it depends on the media (flash drives, floppy disks and SSDs providing easy recovery). If normal recovery fails, that still leaves MRI and microscopes. https://en.wikipedia.org/wiki/Data_erasure
wikipedia is not always reliable but there is information there that I can't explain.
I remember reading about a data recovery technique where the electric charges of the bits on the harddrive are read (or magnetic fields?) and instead of 0 1 1 0 1 you actually have 0.10010 1.10010 1.11111 0.11010 1.10010 and based on the fractional values you can find out that the previous writes for those bytes were: 11111, 00110, 00100, 11111, and 00100, so you can recover more than just the last write. I can't find a link to the article anywhere. I'm sorry. I don't even know what kind of situations it can be used it, I can only remember reading about it.
Usually when you think you're overwriting the file you're really not overwriting every instance of the file on the storage media. If the software you use for overwriting has no write access to the sectors where some copies of the file data are stores it leaves the file recoverable no matter how many times you overwrite it. This is usually the case with USB sticks and SSD drives.
If I said things that are not true, I apologize. I have recovered jpgs from a formatted drive myself, but I'm not sure what formatting the harddrive actually does. I've also recovered files after a format and after the harddrive has been filled with files completely and then some files deleted. Maybe there's a difference between overwriting with zeros and overwriting with files. Maybe the harddrive I used was storing them outside the area where you can write. It's hard to say.