Walgreens, a 111-year-old retail pharmacy, might have the right prescription for staying young as a business: Find new customers through third-party developers, who connect to your services through a public application programming interface (API).

Walgreens did that July 10 with its first publicly published API for third-party developers. It issued an API for its QuickPrints photo development service. It offers one-hour printing in "nearly all" of its 7,907 brick-and-mortar stores. The chain has had its own iPad and iPhone app since 2010, primarily for renewing prescriptions; in March it added the photo printing service.

But the Walgreens app hasn't been downloaded by quite as many of the 74 million iPhone users out there as hoped for.

Walgreens executives believed the potential was there to expand its QuickPrints business. After all, it had read that 27% of all photos taken today are now taken by cell phone users. So this summer it built a software development kit and on July 10 published an API that gave registered developers the ability to connect their applications to the QuickPrints service. Part of the functionality behind the API is to determine the Walgreens store nearest the iPhone user.

[ Want to learn more about how to make your APIs available to third-party developers? See Do's and Don'ts of API Development. ]

One of the first to take advantage of the Walgreens API were the developers behind Pic Stitch, a photo arranging application that's frequently found on the top 30 list of popular iPhone apps. It's been downloaded six million times since its launch 11 months ago.

Alex Keim, Pic Stitch's owner and developer, said the Walgreens API was something he needed to keep Pic Stitch distinguished from the thousands of other photo editing and sharing applications available for free download from the iTunes store. Some observers say there is a total of over 25,000 such apps.

Pic Stitch allows iPhone users to build simple layouts and collages using multiple pictures, adding special effects if they wish. Keim was among the first to add a feature that lets a Pic Stitch user submit a collage to one of the nearby Walgreens for printing.

He said the Walgreens API was well documented and straightforward to adopt. "I was able to implement it in a couple of hours," he said. He regrets the app still only allows one printout per submission by a Pic Stitch. The user should have the option of ordering multiple copies, and he's working on that feature for the next release of the app.

Walgreens' own iPhone app, while offering QuickPrints service, doesn't let users do layouts or combinations of pictures. But with a public API, it doesn't need to think of every option or do the programming to get them into an application. One reason Walgreens made its photo service API public was to tap into the thinking and talents of third-party developers such as Keim.

Keim said he learned of the API before it was published through Aviary, a supplier of photo editing software. Keim is an early adopter of Aviary software. His contacts there advised him his application might be a nice fit with the upcoming Walgreens service. Walgreens published the API July 10. Keim, who had gotten advance information on it, was ready with a new release of Pic Stitch that invoked the service the same day.