Most cameras (if not all) uses the same chip, or a variation of it, to handle the FAT-file system as this makes it cheaper to implement support for cards and so on.
The drawback security-wise, is that they all offer the same functionality. Deleting a file only deletes the header of the file and such the file can easily be reconstructed.
Simply full-formatting the card helps, but with forensic techniques it is possible to get those data back (picking up and amplifying weak electric/magnetic residue). With quick-format only the file table is cleared, content is left untouched.
So what you can do to achieve high security with a common camera is the following:
After you have transferring the pictures use the following procedure:
- Format the card (important: full format, not quick).
- Turn off flash and take as many pictures you can to fill up the card. Point the camera to the sky f.ex. This is to overwrite the old left-over traces with "noise".
- Re-format again with full format
And repeat once more (or twice) to be sure.
This technique is basically what file "shredders" do, only here you do it manually. It's somewhat time-consuming but offer good data security in terms of ability to restore data from the card.