encoding data with a file save?

[dreams4000]

Hey all,
Is there any way with php to encode data with a file save that can be pulled later? The kind of setup I am looking for would allow me to allow a user to download a file, and at the time of download it would also snap with that file encoding that would say for example, this user at this time downloaded the file.. So that at some later point if that file is found floating around, I could look up that data and see who let it float around and when. The key here is that it cant be something the end user could easily just toss out and the file wont be a php file, but multiple types. Any ideas or ways this can be done with php? Thanks All!

[wilku]

It depends on a file type. If it's plain text or any textual data (eg. html) then I can see no way to do it. For binary files, you need to know the structure of a file to add some info dynamically. For example midi has some special midi events concerning copyright - you could use them. Your link should point to php script in which you'd send headers (for midi in this example) then you'd read actual file, send couple of first bytes (identifying mid), send copyright event with text you want and then the rest of a file.
The same is for other types - you just have to know what and when to send. It isn't very reliable though, because users can edit this info anyway (not easily, but they can).