Hi what is your requirement? They may be other approaches which can solve your need, for example you could consider using a content event to hook onto the ContentLoading event.

We have this:

[VisitorGroupCriterion(Category = "Member", DisplayName = "Member role", Description = "")]
    public class UserRoleCriterion : CriterionBase<UserRoleModel>
    {
        public override bool IsMatch(IPrincipal principal, HttpContextBase httpContext)
        {
            if (httpContext?.Session == null)
                return httpContext.Handler is ContentMediaHttpHandler;

            if (SessionHelper.Current == null)
                return false;

            var userRoles = SessionHelper.Current.UserRoles;

            return userRoles != null && userRoles.Any() && userRoles.Any(r => r.Name == Model.Condition);
        }
    }

    public class UserRoleModel : CriterionModelBase
    {
        [Required, DojoWidget(SelectionFactoryType = typeof(RolesSelectionFactory))]
        public string Condition { get; set; }

        public override ICriterionModel Copy()
        {
            return ShallowCopy();
        }
    }

But when loading files the contex is ContentMediaHttpHandler, and it has no session. 

If only I can override the handler with my own, it will work. I works fine with IRenderTemplate<IContentImage> but not with IRenderTemplate<IContentMedia>

Do you have any more info for me? :)

Is your specific requirement to vary the viewing of an image depending on whether someone is in a role or not?

The requirement is to restrict pages, media files (images and documents) to VisitorGroups, and check our role session.

If only IRenderTemplate<IContentMedia> would work...

My solution to change ContentMediaHttpHandler to custom handler:

[ModuleDependency(typeof(EPiServer.Web.InitializationModule))]
public class HandlerInitialization : IInitializableModule
{
    public void Initialize(InitializationEngine context)
    {
        context.Locate.TemplateResolver().TemplateResolved += TemplateCoordinator.OnHandlerTemplateResolved;
    }

    public void Uninitialize(InitializationEngine context)
    {
        ServiceLocator.Current.GetInstance<TemplateResolver>().TemplateResolved -= TemplateCoordinator.OnHandlerTemplateResolved;
    }

    public void Preload(string[] parameters)
    {
    }
}

Change Template:

public class TemplateCoordinator
{
     public static void OnHandlerTemplateResolved(object sender, TemplateResolverEventArgs args)
     {
            if (args.SelectedTemplate == null ||
                args.SelectedTemplate.TemplateType != typeof(ContentMediaHttpHandler))
                return;

            var mediaHandler = args.SupportedTemplates
                .SingleOrDefault(r => r.Name.Contains("CustomContentMediaHttpHandler") 
                    && r.TemplateTypeCategory == args.SelectedTemplate.TemplateTypeCategory);

            if (mediaHandler != null)
                args.SelectedTemplate = mediaHandler;
        }
}

Great you managed to solve it and thanks for sharing the soluton :)!