Calling AGPL code with a PHP Script

Question

I made an AGPL-3.0 project in Python3 that fills in missing regions of images.

Someone made a website that uses the AGPL code on their server. A user uploads an image on their website, the image is saved to a folder on their server, and, the AGPL Python3 code (which processes the image) is executed with a PHP script.

They share their modifications to the AGPL Python3 code but do not share the PHP script or any other server/website code.

Is sharing the modified AGPL Python3 code sufficient? If not, what needs to be done to comply with AGPL?

Answer 1

The distribution requirements of the AGPL license apply to derived works, not to works that merely co-exist or interact with the AGPL work.

The big question is when is a work a derived work. The FSF (the authors of the AGPL license) draw that line at the process boundary and a concept called "at arms length communication". In a nutshell, it comes down to if it is possible to create a drop-in replacement for your Python3 code that does not contain any of your (A)GPL-licensed code.

Generally, this is possible if the PHP and Python code only communicate using the normal command-execution mechanisms of the underlying OS and don't depend on particular data structures being exchanged. In that case, it is indeed sufficient to publish only the (modified) Python code.