A (Android Studio Module) demo for showing how a Android WebView uploads image files from gallery or photography acquiescently. I had tested it in several android devices whose system versions are from 4.2.2 to 6.0.1. It still doesn't work in some devices of Android Kitkat(4.4.4).

And there are some resolvations you could consider:

1. User Cordova instead of System WebView.
2. Use JS to invoke native method of uploading files.