I am working on an open source project for an academic competition. Our customer requires us to use for our product the LGPL v.2.1. We have to use QR codes in part of our application, and we found different libraries, all licensed under the Apache License v.2.0. I read that the LGPL and the Apache License are incompatible in these versions.
My question is: does the incompatibility applies only when using the code from both, or also in using the library without touching the source code? That is, can we use an Apache library in an LGPL project, if we use it as it is, without incorporating, but just using/linking to it?
Thanks to all who want to answer and help.