QByteArray frontCamera = QCamera::availableDevices()[1];
_camera = new QCamera(frontCamera);
_camera->setCaptureMode(QCamera::CaptureStillImage);
_stillImageCapture = new QCameraImageCapture(_camera);

qDebug() << "Resolutions: " << _stillImageCapture->supportedResolutions();

On C7 the code above outputs only QSize(320, 240), although the device specs for C7 say that it should be capable of 640x480 as well.