uses
  GDIPAPI, GDIPOBJ;

type
  // we need to subclass the TGPImage to access the protected NativeImage field
  TGPImage = class(GDIPOBJ.TGPImage)
  public
    function GetPixel(X, Y: Integer; out Color: TGPColor): TStatus;
  end;

implementation

{ TGPImage }

function TGPImage.GetPixel(X, Y: Integer; out Color: TGPColor): TStatus;
begin
  Result := SetStatus(GdipBitmapGetPixel(GPBITMAP(NativeImage), X, Y, Color));
end;