Most of the scan doc package out there cost a fortune. Last time I looked into one it cost tens of thousands euros a year.
Getting Opencv package to play nicely with RN out-of-box is almost impossible. Part of the reason is also that I try to avoid using install OpenCV manager for Android. Believe me I had tried make it as dummy as possible to the best of my knowledge. But the reality is setting up opencv to work nicely with Android itself is a challenging enough task.
I suggest you look at a few examples to understand how OpenCV works with Android first then proceed to manual installation. https://blog.nishtahir.com/2015/11/11/setting-up-for-android-ndk-development/
Try out my Android Native Scan Doc sample if you want to first check out how the scan doc helps you to crop a doc in image.
Again, I am open to have some help from the community to improve the package documentation.
I myself unfortunately is tied up with other work of my own. Will look into this seriously once I got time and resource. Thanks.
$ npm install react-native-scan-doc --save
Mostly automatic installation (You still need to setup OpenCV yourself, read more)
$ react-native link react-native-scan-doc
##Features
- Scan document.
 - Perspective Transform.
 
- Scan document.
 - Perspective Transform.
 
##Requirements
API 16+
iOS 8+
RN 0.38+
- In XCode, in the project navigator, right click 
Libraries➜Add Files to [your project's name] - Go to 
node_modules➜react-native-scan-docand addRNScanDoc.xcodeproj - In XCode, in the project navigator, select your project. Add 
libRNScanDoc.ato your project'sBuild Phases➜Link Binary With Libraries - Run your project (
Cmd+R)< 
- Open up 
android/app/src/main/java/[...]/MainActivity.java 
- Add 
import my.fin.RNScanDocPackage;to the imports at the top of the file - Add 
new RNScanDocPackage()to the list returned by thegetPackages()method 
- Append the following lines to 
android/settings.gradle:include ':react-native-scan-doc' project(':react-native-scan-doc').projectDir = new File(rootProject.projectDir, '../node_modules/react-native-scan-doc/android') - Insert the following lines inside the dependencies block in 
android/app/build.gradle:compile project(':react-native-scan-doc') 
import RNScanDoc from 'react-native-scan-doc';
// TODO: What do with the module?
RNScanDoc;