in Hands-on lab/lab-files/src/TollBooth/TollBooth/FindLicensePlateText.cs [98:106]
private static ByteArrayContent GetImageHttpContent(byte[] imageBytes)
{
var content = new ByteArrayContent(imageBytes);
// Add application/octet-stream header for the content.
content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
return content;
}