I took the above answers and made a bit of a wrapper extension:
    public static MvcHtmlString ActionImageLink(this HtmlHelper helper, string src, string altText, UrlHelper url, string actionName, string controllerName)
        {
            return ActionImageLink(helper, src, altText, url, actionName, controllerName, null, null);
        }
        public static MvcHtmlString ActionImageLink(this HtmlHelper helper, string src, string altText, UrlHelper url, string actionName, string controllerName, Dictionary<string, string> linkAttributes, Dictionary<string, string> imageAttributes)
        {
            return ActionImageLink(helper, src, altText, url, actionName, controllerName, null, linkAttributes, imageAttributes);
        }
        public static MvcHtmlString ActionImageLink(this HtmlHelper helper, string src, string altText, UrlHelper url, string actionName, string controllerName, dynamic routeValues, Dictionary<string, string> linkAttributes, Dictionary<string, string> imageAttributes)
        {
            var linkBuilder = new TagBuilder("a");
            linkBuilder.MergeAttribute("href", routeValues == null ? url.Action(actionName, controllerName) : url.Action(actionName, controllerName, routeValues));
            var imageBuilder = new TagBuilder("img");
            imageBuilder.MergeAttribute("src", url.Content(src));
            imageBuilder.MergeAttribute("alt", altText);
            if (linkAttributes != null)
            {
                foreach (KeyValuePair<string, string> attribute in linkAttributes)
                {
                    if (!string.IsNullOrWhiteSpace(attribute.Key) && !string.IsNullOrWhiteSpace(attribute.Value))
                    {
                        linkBuilder.MergeAttribute(attribute.Key, attribute.Value);
                    }
                }
            }
            if (imageAttributes != null)
            {
                foreach (KeyValuePair<string, string> attribute in imageAttributes)
                {
                    if (!string.IsNullOrWhiteSpace(attribute.Key) && !string.IsNullOrWhiteSpace(attribute.Value))
                    {
                        imageBuilder.MergeAttribute(attribute.Key, attribute.Value);
                    }
                }
            }
            linkBuilder.InnerHtml = MvcHtmlString.Create(imageBuilder.ToString(TagRenderMode.SelfClosing)).ToString();
            return MvcHtmlString.Create(linkBuilder.ToString());
        }
has made it easier for me anyway, hope it helps someone else.