To implement the required code, in your project, select the custom widget class. In this case, this is the FancyImageGallery.ascx.cs class. Paste the following code and then build your project:
  using System;
 using System.Linq;
 using System.Web.UI;
 using Telerik.Sitefinity.GenericContent.Model;
 using Telerik.Sitefinity.Modules.Libraries;
   
 namespace SitefinityWebApp.CustomImageGallery
 {
     public partial class FancyImageGallery : System.Web.UI.UserControl
     {
         protected void Page_PreRender(object sender, EventArgs e)
         {
             InitPage();
         }
   
         protected void Page_Load(object sender, EventArgs e)
         {
             if (!Page.IsPostBack)
             {
                 var librariesManager = LibrariesManager.GetManager();
                 var images = librariesManager.GetImages().Where(i => i.Status == ContentLifecycleStatus.Live);
                 this.ImageRepeater.DataSource = images;
                 this.ImageRepeater.DataBind();
             }
         }
   
         private void InitPage()
         {
             var scriptManager = ScriptManager.GetCurrent(Page);
   
             if (scriptManager == null) return;
   
             // Adding jQuery version 1.4.4 from a CDN
    
             // Adding the Fancybox library
             scriptManager.Scripts.Add(new ScriptReference { Path = "~/CustomImageGallery/fancybox/jquery.fancybox-1.3.4.pack.js" });
   
             // Adding a custom Javascript resource 
             scriptManager.Scripts.Add(new ScriptReference { Path = "~/CustomImageGallery/FancyImageGallery.js" });
         }
     }
 }