using System;

using System.Xml;

using System.Linq;

using System.Xml.Linq;

using System.Collections.Generic;

using System.Linq;

using System.Linq.Expressions;

public class Program {

    public static void Main() {

        string stringXml = @"<user>

                                 <image size='small'>http://userserve-ak.last.fm/serve/34/101313093.jpg</image>

                                <image size='medium'>http://userserve-ak.last.fm/serve/64/101313093.jpg</image>

                                <image size='large'>http://userserve-ak.last.fm/serve/126/101313093.jpg</image>

                                <image size='extralarge'>http://userserve-ak.last.fm/serve/252/101313093.jpg</image>

                                </user>";

        XElement xdoc = XElement.Parse(stringXml);

        var result= xdoc.Descendants("image")

                .Where(x => x.Attribute("size").Value == "large")

                .Select(x => new User{ Image =  x.Value });

        foreach (var item in result) 

            Console.WriteLine(item.Image);

    }

    public class User {

        public string Image {get;set;}

    }

}