The .cmd file is the file that's called "StartJAlbum.cmd", It's located in jAlbum's installation folder. If you have installed the early Java 9, then you can launch jAlbum on Java 9 using that file. Just double-click it. Now image scaling should work fine.
woohooo!! Finally usable once again!
You should advertize the fix (with steps) on the JAlbum site.
Can I even suggest you display a (written in big letters!) message when 4K resolution is detected at startup and java 9 is not enabled?!