Want to spawn process from Windows PHP

[Alfred Whitney]

I wanted to write some code purely on Linux, but unfortunately the
document scanner drivers are non-existent for the high-end commercial
document scanners. So, I had to port my Linux PHP project to Windows
PHP (WAMP). There, I found a scanning tool (Kodak Image Scan -
imgscan.ocx) that I can put on a VB form, tell it to scan some
documents into a TIF file, and then shut down.

I can run this VB app at command line just fine, but when I run it from
either a popen(), system(), or exec() call, it won't detach from the
PHP page. Instead, it just sits there. I can see the VB exe I made is
being loaded properly in RAM, but unfortunately it sticks and won't
unload on its own, nor will it tell the scanner to engage. I have to
kill the VB exe and then the PHP page continues.

What's the way to spawn a detached process from PHP on Windows?