Terms of the deal were not announced. Snapjoy allows users to view and collect their photos in one location, whether they originate in a camera, PC , smartphone or such sites as Flickr. The service provides full-screen slideshows and the ability to download entire albums from a site if given permission by the photos' owner. Both Snapjoy and Dropbox are alumni of Y Combinator, the Mountain View, Calif.-based startup accelerator.

'100 Million People'

A week ago, Dropbox announced a major update for its iOS app, which features a new user interface and new capabilities for handling photos, such as a Photos tab with a timeline view of automatically uploaded media. In October, Dropbox updated its Android app with photo-sharing and a Photos tab.

On its corporate blog, Snapjoy said that combining forces will allow it to "leverage the technology and scale of their platform and focus on what matters -- delivering an incredible photo experience to over 100 million people," meaning the population of Dropbox users.

Snapjoy co-founder Michael Dwan told news media that he decided to sell because of the scale offered by Dropbox. In 2011, Dropbox had revenue of $240 million from 50 million paying users.

For the moment, Snapjoy said it will not be accepting new signups, but existing users can continue to use the service. Within a few weeks, it expects to make additional announcements about changes in the service.

'Mindshare and Category Leader'

A week ago, Dropbox announced the acquisition of Audiogalaxy, a music streaming app that allowed users to receive their playlist-based music from their own PC, on their smartphone. Bit by bit, Dropbox is adding capabilities to its storage platform that offers services to its users beyond simply storage.

The Snapjoy acquisition, for instance, enhances Dropbox's evolution into a photo center with a portfolio of capabilities. Online storage by itself has become largely a commodity service, differentiated primarily by prices and storage amounts. The growing list of cloud-based sharing and storage services includes Microsoft 's SkyDrive, Google's Drive, Samsung's S-Cloud service, Apple's iCloud, Amazon 's Cloud Drive, Box and SugarSync.

Ross Rubin, principal analyst with Reticle Research, said Dropbox has been "the mindshare and category leader" in cloud-based storage, "especially in the consumer space, while Box has been focusing on the enterprise ."

He noted that, previously, Dropbox had been "a somewhat vanilla storage service," but now it's seeking to become less generic with such services as sharing and presentation for photos stored there. Photos are particularly appropriate, Rubin said, given that they are produced in volume by smartphones, and their proliferation and sharing means that the average photo-using customer might well seek to obtain more storage on Dropbox.

In August, Dropbox added new security measures after acknowledging that it had been hacked.