even polyglot image/executables are usually _mostly_ two files mashed together. some cleverness is always required to construct a header that is valid for both

even polyglot image/executables are usually _mostly_ two files mashed together. some cleverness is always required to construct a header that is valid for both formats, but then the trick is usually to make the executable jump past the image data (or, for interpreted languages, comment out the image data) and then store the executable payload at the end of the file.