Using Images for Category Menu Links

I am trying to modify the category menu to use images instead of text. I am having some difficulty since the links are generated dynamically. I am assuming I will need to add some code to the CreateChildMenu method in the CategoryNavigation.ascx.cs file to have something like

var link = new NopCommerceLi();
if (category.CategoryId = 5)
                {
                    phCategorie.Controls.Add(LINK OR IMAGE);  
                }
                else if (category.CategoryId = 6)
                {
                    phCategorie.Controls.Add(NEXT LINK OR IMAGE);
                }

I am not sure what to enter to generate the image however. I am new to C# and NopCommerce so and help is greatly appreciated!