Called Instagram Direct, the feature is available for Apple and Android phones, CEO Kevin Systrom said in New York City. Users can choose up to 15 people who follow them on Instagram to share photos or videos.
Previously, the only way to share content on Instagram was to post it to your feed, which can be either visible to everyone or locked so only people you approve can see it.
The new tool comes as popularity of messaging apps like Snapchat and WhatsApp is growing. On Tuesday, Twitter also updated its direct messaging tool to let users send photos and videos to one another for the first time.
Forrester Research analyst Julie Ask called the messaging tool a "catch up move" for Instagram, in a blog post, noting that apps such as WeChat already let people share videos, photos, messages and other content.
To use Instagram Direct, download the latest update to the app, and upload or snap a photo the way you normally would. Once you're done applying old-school filters, tagging your buddies and adding a caption if you wish, you'll get the option to either share with "followers" or "direct." Tapping the latter will bring up suggested followers to send the photo to, or let you pick from your list of followers.
Once you send the photo, a green check mark will appear if the recipient has seen it, replaced by a heart if they "liked" it. It is possible to send photos to people who don't follow you, but it'll appear as a pending request and won't go into their inbox. They can tap "X" and they won't get a direct message from you again -- or tap a checkmark and it'll go into their inbox.
Systrom said the reason for the 15-recipient limit is to make the feature about "moments you share with friends" and "not about spamming everyone you know."
Sterne Agee analyst Arvind Bhatia thinks the new feature will help Instagram compete with Snapchat, the disappearing-message app that Facebook reportedly tried and failed to buy for $3 billion recently.
Instagram has more than 150 million users -- up from 80 million at the start of this year -- and more than half of them use it every day, Systrom said.