File de-merge in cmd?

[Synoptic]

Yo!

I've been recently looking for a solution to this "problem" but couldn't find any lol

I merged 2 files together with the command "copy /b file1 + file2 file 3" in command promt and now I want to separate those 2 files.

How do I do it?

Please help.

Thanks in advance.

EDIT:
Ohh I should mention that I merged 2 JPG files.