Just to keep down clutter for npc portraits, I have started using a handout with a list of links to npc portraits. All the portraits are archived so that they aren't in the folder structure at all. I keep the list available to players so they can click a link to bring up a portrait. The player view has npcs categorized by location or association, so they are easier for players to find. Anyone I want to keep to myself, I keep in the GM notes section of the list handout. Of course, all those can be categorized however you want, since it only shows on the GM view of the handout. If this is a "disposable" npc, then it might not be worth this much setup. I generally make my players suffer without portraits for random, one time only people they meet.