Tool for automatically resaving media nodes in Umbraco v6. Add to your dashboard.config to gain easy access to this tool.

RebuildMediaCacheTool.ascx

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="RebuildMediaCacheTool.ascx.cs" Inherits="My.Website.Dashboard.RebuildMediaCacheTool" %>
<div class="dashboardWrapper">
    <h2>Rebuild Media Cache</h2>
    <img src="/umbraco_client/Dashboards/ExamineManagementIco.png" alt="" class="dashboardIcon" />
    <asp:MultiView ID="MainView" runat="server">
        <asp:View ID="InitialView" runat="server">
            <asp:Button ID="RebuildButton" Text="Rebuild Media Cache" runat="server"/>
        </asp:View>
        <asp:View ID="CompleteView" runat="server">
            <p>Rebuild complete!</p>
            <p><%: MediaCount %> Media Items cache rebuilt</p>
        </asp:View>
    </asp:MultiView>
</div>

RebuildMediaCacheTool.ascx.cs

using System;
using System.Linq;
using Umbraco.Core.Models;
using Umbraco.Web.UI.Controls;

namespace My.Website.Dashboard {
    public partial class RebuildMediaCacheTool : UmbracoUserControl {
        public int MediaCount { get; set; }

        protected void Page_Load(object sender, EventArgs e) {
            if (IsPostBack == false) {
                MainView.SetActiveView(InitialView);
            }

            RebuildButton.Click += OnRebuildButtonClick;
        }

        private void OnRebuildButtonClick(object sender, EventArgs e) {
            var rootNodes = Services.MediaService.GetRootMedia();

            foreach (var rootNode in rootNodes.Where(x => x.Trashed == false)) {
                Services.MediaService.Save(rootNode);
                MediaCount++;

                foreach (var ancestor in rootNode.Descendants().Where(x => x.Trashed == false)) {
                    Services.MediaService.Save(ancestor);
                    MediaCount++;
                }
            }

            MainView.SetActiveView(CompleteView);
        }
    }
}