GetGravatarURL.cs

string emailHash;
using (var md5 = MD5.Create())
{
    var sb = new StringBuilder();
    var data = md5.ComputeHash(Encoding.UTF8.GetBytes("myemail@email.com"));
    
    foreach (byte t in data)
    {
        sb.Append(t.ToString("x2"));
    }
    
    emailHash = sb.ToString();
}

return $"http://www.gravatar.com/avatar/{emailHash}?s=30&d=mm";