Question

How to do it with razor helper method?

The answer at question linked below uses extension method.
Action Image MVC3 Razor

Answer 1

I’m not really sure why an extension method isn’t suitable, but something like this should work:

@helper ActionImage(string action, object routeValues, string imagePath, string alt) {
    <a href="@Url.Action(action, routeValues)">
        <img src="@Url.Content(imagePath)" alt="@alt">
    </a>
}

That is just off the top of my head, so your milage may vary. You should also be able to use the implementation provided in the question as a @functions { } block rather than an extension method as well.