using System;
using System.Collections;
using System.Text.RegularExpressions;
public class MyClass
{
public static void Main()
{
String input = "<img src=\"images/1.gif\" border=\"0\">";
String pattern = "<img\\s+[^(src>)]*src\\s*=\\s*[\"']{0,1}(?<SRC>[^(\\s\"'>)]*)[\"']{0,1}\\s{0,1}[^>]*>";
Regex r = new Regex(pattern, RegexOptions.IgnoreCase);
String result = "";
result = r.Replace(input, "${SRC}");