In Android version missing WebP format (no lib in relative directory like others platform). I used correctly QTPLUGIN += qwebp and QImageReader::supportedImageFormats() to verify this.

PS: this library/plugin is present on iOS platform (I saw on http://download.qt-project.org/online/qtsdkrepository/mac_x64/ios/qt5_53/qt.53.ios/5.3.0-0qt5_addons.7z) but not in Android platform (I saw on http://download.qt-project.org/online/qtsdkrepository/mac_x64/android/qt5_53/qt.53.android_armv7/5.3.0-0qt5_addons.7z)