GetImageInHtmlSnippet.cs

public static async Task<string> GetImageInHtmlNotice(string url)
{
    var page = await GetNodeHtml(url);
    string selector = string.Empty;
   
    selector = ".image img";

    var consulta = (from item in page.QuerySelectorAll(selector)
                    select item).FirstOrDefault();
    
    string result = string.Empty;
    if (consulta != null)
    {
        result = consulta.Attributes["src"].Value;                
    }

    return result;
}

GetNodeHtmlSnippet.cs

public static async Task<HtmlAgilityPack.HtmlNode> GetNodeHtml(string url)
{
    var doc = new HtmlAgilityPack.HtmlDocument();
    var client = new System.Net.Http.HttpClient();
    var stream = await client.GetStreamAsync(url);
    doc.Load(stream);
    var page = doc.DocumentNode;
    return page;
}