Editors can not recognize the encrypted comment.
Editing can destroy the information.
Why do this instead of PGP? PGP can be broken with enough computer power. The advantage of this technique is that they do not even know their is a code to break. Therefore, even 20 years from now, people may not be able to retreive the secret information, not because their computers are not powerfull enough to break your encryption, but because they do not realize the information is there to find.
You could get a slighlty less effective but similar result simply by renaming your secret information something like "image.retrieval.dll" and hoping that no one bothers to try and decrypt it. But by puting it into a regular file, people are less likely to try and break the code.