You can access the pixel data from a captured image in Native code through the ICameraCaptureFrameNative. The object that implements the interface is obtained through COM. Once you have obtained the object, use MapBuffer() to access the BYTE * array.
Note that the pixel data obtained this way is in NV12 format, not a JPEG or RGB as one would expect.
#include <Windows.Phone.Media.Capture.Native.h>
CameraCaptureFrame^ frame = m_cameraCaptureSequence->Frames->GetAt(0);
pNativeFrame = NULL;
HRESULT hr = reinterpret_cast<IUnknown*>(frame)->QueryInterface(__uuidof(ICameraCaptureFrameNative ), (void**) &pNativeFrame);
create_task( m_camera->PrepareCaptureSequenceAsync(m_cameraCaptureSequence) ).wait();
create_task( m_cameraCaptureSequence->StartCaptureAsync() ).then([this]()
{
DWORD bufferSize =0;
BYTE * pBuffer = NULL;
pNativeFrame->MapBuffer(&bufferSize, &pBuffer); // Pixels are in pBuffer.
// Unmap() the buffer before capturing another image.