Instagram will start to introduce advertising to its stories feature as it becomes more popular, stepping up competition with Snap Inc. Facebook Inc.’s Instagram said it now has 150 million daily users on the stories feature of its photo-sharing site that was inspired by a popular Snapchat product, which broadcasts short videos that disappear after they’re viewed, or after 24 hours. Instagram’s number for stories matches the statistic Snapchat gives for its total daily global audience.