how to get src value from img tag in c#

var shieldHomeContainer = nodeCollection.SelectSingleNode("//img").Attributes["src"].Value;

string str = "<div> <img src=\"https://i.testimg.com/images/g/test/s-l400.jpg\" style=\"width: 100%;\"> <div>Test</div> </div>";

// Get the index of where the value of src starts.
int start = str.IndexOf("<img src=\"") + 10;

// Get the substring that starts at start, and goes up to first \".
string src = str.Substring(start, str.IndexOf("\"", start) - start);