Over the last several weeks, a few different emoji-related App Review stories have been shared by developers on Twitter. Though it's common practice to use emoji throughout an app's interface, Apple has begun rejecting some apps for just this reason.
Emojipedia founder Jeremy Burge researched the issue and summarized what seems to be a shift in Apple's handling of emoji use. In a piece titled "Apple's Emoji Crackdown" he walks through his current understanding of what's permissible regarding emoji use, and what isn't – though with the caveat that none of this has been officially addressed by Apple yet. He concludes:
It would be a shame to see emojis banished from all apps due to potentially over-zealous app reviewers.
Using an emoji as a core part of an app's UI, or in-game character seems to be a fairly clear overstepping of the mark, and now that Apple has begun enforcing this, I don't expect that side of things to change.
It's understandable there is much confusion about this right now, especially as the Apple Color Emoji font until now has been treated by many as a font like any other. If...thought about as "a set of images created and owned by Apple", the terms for what seems reasonable do shift.
Despite the lack of word from Apple on an official policy change, the signs don't look good. Apple owns the rights to its emoji designs, and there is currently no way for developers to license those designs, so we may begin seeing a lot less emoji use in apps soon.