using System;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var s = @"this is my text here is a link http://d...content-available-to-author-only...f.com and my is /images/dd.gif";
        var regex = new Regex(@"\S*/images\S*|(?<!\S)((?:(?:https?|ftp)://)?[\w-]+(?:(?:\.[\w-]+)+)(?:[\w.,@?^=%&:/~+#-]*[\w@?^=%&/~+#-])?)");
        var result = regex.Replace(s, match => match.Groups[1].Success ? "" : match.Value);
        Console.WriteLine(result);
	}
}

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