[DllImport(@"stasmstasm_dll.dll", CallingConvention = CallingConvention.Cdecl)]
    internal static extern void AsmSearchDll
    (
        [Out] out Int32 pnlandmarks,
        [Out] out Int32[] landmarks,
        [In, MarshalAs(UnmanagedType.LPStr)] String image_name,
        [In, MarshalAs(UnmanagedType.LPStr)] String image_data,
        [In] Int32 width,
        [In] Int32 height,
        [In] Int32 is_color,
        [In, MarshalAs(UnmanagedType.LPStr)] String conf_file0,
        [In, MarshalAs(UnmanagedType.LPStr)] String conf_file1
    );

    public void SearchFacialFeatures()
    {
        string image_name = "image-5.jpg"; // imagePath;
        var image = new Image<Bgr, byte>(image_name).Convert<Gray, byte>();

        int pnlandmarks = 0;
        var landmarks = new int[500];

        var imageData = Marshal.PtrToStringAnsi(image.MIplImage.imageData);
        int imgWidth = image.Width;
        int imgHeight = image.Height;
        int is_color = 1;
        string confile_file0 = Path.GetFullPath(@"datamu-68-1d.conf");
        string config_file1 = Path.GetFullPath(@"datamu-76-2d.conf");
        string sDataDir = @"stasmdata";


        AsmSearchDll(out pnlandmarks, out landmarks, image_name, imageData, imgWidth, imgHeight, 1, null, null);

        MessageBox.Show(image_name);
    }

AsmSearchDll(out pnlandmarks, out landmarks, image_name, imageData, imgWidth, imgHeight, 0, null, null);

void AsmSearchDll (
int *pnlandmarks,          // out: number of landmarks, 0 if can't get landmarks
int landmarks[],           // out: the landmarks, caller must allocate
const char image_name[],   // in: used in internal error messages, if necessary
const char image_data[],   // in: image data, 3 bytes per pixel if is_color
const int width,           // in: the width of the image
const int height,          // in: the height of the image
const int is_color,        // in: 1 if RGB image, 0 if grayscale
const char conf_file0[],   // in: 1st config filename, NULL for default
const char conf_file1[])   // in: 2nd config filename, NULL for default, "" if none

const char *image_name = "../data/test-image.jpg";

IplImage *img = cvLoadImage(image_name, CV_LOAD_IMAGE_COLOR);
if(img == NULL) {
    printf("Error: Cannot open %sn", image_name);
    return -1;
}
// sanity checks (AsmSearchDll assumes imageData is vector of b,r,g bytes)

if(img->nChannels != 3 || img->depth != IPL_DEPTH_8U ||
        img->origin != 0 || img->widthStep != 3 * img->width) {
    printf("Error: %s is an unrecognized image typen", image_name);
    return -1;
}

// locate the facial landmarks with stasm

int nlandmarks;
int landmarks[500]; // space for x,y coords of up to 250 landmarks
AsmSearchDll(&nlandmarks, landmarks,
             image_name, img->imageData, img->width, img->height,
             1 /* is_color */, NULL /* conf_file0 */, NULL /* conf_file1 */);

[DllImport(@"stasmstasm_dll.dll", CallingConvention = CallingConvention.Cdecl, CharSet=CharSet.Ansi)]
internal static extern void AsmSearchDll
(
    [Out] out Int32 pnlandmarks,
    [Out] Int32[] landmarks,       // <-- the `out` keyword is removed
    [In, MarshalAs(UnmanagedType.LPStr)] String image_name,
    [In] IntPtr image_data,        // <-- should not be passed as string
    [In] Int32 width,
    [In] Int32 height,
    [In] Int32 is_color,
    [In, MarshalAs(UnmanagedType.LPStr)] String conf_file0,
    [In, MarshalAs(UnmanagedType.LPStr)] String conf_file1
);