After launching in November as a gorgeous app for making social collages, the iPad app Mixel received an update today that will let you create private image threads, instead of having every Mixel creation public.

With increased privacy, users will hopefully have fewer inhibitions about using personal photos to create Mixels, co-founder Khoi Vinh told VentureBeat in an interview earlier this week. Vinh, a former design director for the New York Times, noticed that users were particularly hesitant to use personal photos in the past. That’s not too surprising, since any public Mixel collage can be easily remixed by others on the service.

You can think of Mixel like an Instagram for collages — it lets you effortlessly create collages, or Mixels, using your own images and photos from around the web, or by tweaking someone else’s existing work. You can share your digital finger art with friends on the service or push it to the web or other social networks for all to see. Mixel is a product of Lascaux, a company co-founded by Vinh and creator Scott Ostler.

With a private Mixel thread, only you and the people you invite will be able to edit and share a collage. It’s also better for collaboration — for example, designers using the service wouldn’t want their work leaking out early.

Before Mixel took shape, Vinh initially wanted to create a social drawing app where multiple people could draw at the same time — but the performance anxiety with simultaneous drawing made that idea untenable. With the initial release of the app, Vinh learned that using personal photos and working in public led to performance anxiety of another sort.

With the latest update, the app now also supports the new iPad’s Retina Display. Vinh said that migrating the app wasn’t a huge ordeal, particularly because most Mixel users weren’t using high-resolution images to begin with.

Since it launched last November, Mixel has developed a strong following of core users. The company isn’t talking user figures yet, but Vinh told me that its engagement is “healthy.” Almost half of Mixel’s active users step into the app once a day, and the app is outperforming similar apps in session length by three times.

New York City-based Mixel has raised $700,000 so far, including $600,000 from a seed round that included Polaris Venture Partners, Betaworks, and Allen & Company.

Mixel image via Akira Hashiguchi