Zxing is the best. You can use it without installing the zxing app. You can use Zxing. It's a better customisable QR Scanning library. Something that can be easy to implement and have more control for the developer. I found some links
Alternative to zxing QR reader library for Java/Android?
Better use this :https://github.com/LivotovLabs/zxscanlib
https://code.google.com/p/android-quick-response-code/
You can use it without installing application. Just extent the CaptureActivity Class after adding zxing as library project.