Retrieve image from MSCRM 2013

First you need to get the service object

to get service object follow the below link:
http://raju2565.blogspot.in/2014/07/mscrm-online-authentication.html

Entity _account = new Entity("account");
        string binaryImageQuery = String.Format(@"<fetch mapping='logical'>
                                  <entity name='{0}'>
                                    <attribute name='sample_name' />
                                    <attribute name='entityimage' />
                                  </entity>
                                </fetch>", _account);

        EntityCollection binaryImageResults = service.RetrieveMultiple(new FetchExpression(binaryImageQuery));


        Console.WriteLine("Records retrieved and image files saved to: {0}", Directory.GetCurrentDirectory());
        foreach (Entity record in binaryImageResults.Entities)
        {
            String recordName = record["sample_name"] as String;
            String downloadedFileName = String.Format("Downloaded_{0}", recordName);
            byte[] imageBytes = record["entityimage"] as byte[];
            var fs = new BinaryWriter(new FileStream(downloadedFileName, FileMode.Append, FileAccess.Write));
            fs.Write(imageBytes);
            fs.Close();
            Console.WriteLine(downloadedFileName);
        }