On earlier releases, I packed ecm.exe with the releases, without a .bat 
file or instructions of how people could generate the final .cdi file. 

This is an alternative I've been using on newer releases. It's an 
utility that uses ecm code to generate the image file, but it comes with 
a custom menu and built-in functionality for applying patches. If you 
check the code you'll be able to find out the patch file format. 

- create_patch.exe is an auxiliary tool to create the patch for the tool 
automatically. It will compare two files, and generate the patch based 
on this.