Display anti-leech pictures through server transfer

 I have a function to collect useful content from other people's websites. There is a picture link in the collected content, which can be opened separately, but it cannot be displayed on my website. The error message is:

Obviously, there is anti-theft chain function, which can only be opened on his website. This is easy to handle, a few lines of code

Add a relay request to my website, get the image stream on the server, and output it to my client (localhost):

// GET: Home/PickUpImage?src=http://xxxx:yy
public async Task<ActionResult> PickUpImage(string src)
{
    if (string.IsNullOrEmpty(src)) return HttpNotFound();
    var stream = await HttpHelper.GetAsync(src);
    return File(stream, "image/png");
}

Among them, HttpHelper is my tool class for operating HTTP requests (it must be a singleton mode or a static method class, and cannot be made into an instance class), which is implemented through HttpClient, and remembers cookies (key points) for each request. Part of the code is implemented:

public class HttpHelper
    {
        private static readonly HttpClient _hc;
        static HttpHelper()
        {
            _hc = new HttpClient(new HttpClientHandler { AllowAutoRedirect = false, UseCookies = true });
            _hc.MaxResponseContentBufferSize = 2 * 1024 * 1024; //2MB
            _hc.DefaultRequestHeaders.Add("user-agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36");
            _hc.Timeout = new TimeSpan(0, 1, 0); //1 minute
        }
        public static async Task<Stream> GetAsync(string url)
        {
            if (url.StartsWith("https", StringComparison.OrdinalIgnoreCase))
            {
                ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12 | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls;
                ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(CheckValidationResult);
            }
            return await Client.GetStreamAsync(url);
        }
}

In this way, the src address of img on the page is given by

https://cdn.whatismyipaddress.com/images/flags/mo.png

change to

http://localhost:3721/Home/PickUpImage?src=https://cdn.whatismyipaddress.com/images/flags/mo.png

The picture will show