Though a picture can be worth a thousand words, a few words here and there can explain context, so the WWMX researchers added pop-tags to the application. "Pop-tags are the idea that anyone can write on your photo," says Roseway. "You can also add links this way. Maybe you put up a photo of a shop that has an online store, you can add the URL. Or the tags could be used for an event and everyone who went could comment on it.