Emoji are generally rendered on your device by locally stored fonts licensed to the end user for use with their operating system. In this case copyright is irrelevant as your software is not distributing the artworks any more than my answer to this question is distributing the Arial typeface.
If you need to render Emoji on a system that has no such font, then you're looking at copyright issues as you'll need to distribute original artworks.
To distribute fonts outside of a licensed OS or create and distribute image files from them would be subject to the license that comes with the OS and/or its font files.
For example the Gemoji project has made bitmap version of Apple Emoji and is copyright of Apple - whether that means you can use them as long as you add a copyright notice or not, I cannot tell you.
By contrast, Android's Emoji font is licensed under the Apache 2 license, so I think (and I'm not a lawyer) that you may use the font according to those terms in your own work. I am using Android Emoji as a web font here if you're interested.
Worth noting too is the Phantom Emoji project which is creating an open source set of full colour emoji.
Emoji are just fancy emoticons, and last I checked, emoticons aren't generally protected by copyright (because of their small size; to my knowledge, you normally can't copyright individual words, which is what emoticons/emoji are equivalent to. You can trademark them, though). However, I doubt they could be properly trademarked, either, considering their generic nature/common usage. A logo/etc. that contains emoji could probably be trademarked (and it's almost certain that at least one has, though I can't think of any off the top of my head), but I don't believe the emoji itself could.
At the very least, you're as likely to encounter legal trouble when using emoji as you are when quoting an internet meme.
If you are using these from font then no, but if you copied these to your project resources - add notice to your about window. If you want to use them on Windows (from Mac to Windows) you must.
Emoji are generally rendered on your device by locally stored fonts licensed to the end user for use with their operating system. In this case copyright is irrelevant as your software is not distributing the artworks any more than my answer to this question is distributing the Arial typeface.
If you need to render Emoji on a system that has no such font, then you're looking at copyright issues as you'll need to distribute original artworks.
To distribute fonts outside of a licensed OS or create and distribute image files from them would be subject to the license that comes with the OS and/or its font files.
For example the Gemoji project has made bitmap version of Apple Emoji and is copyright of Apple - whether that means you can use them as long as you add a copyright notice or not, I cannot tell you.
By contrast, Android's Emoji font is licensed under the Apache 2 license, so I think (and I'm not a lawyer) that you may use the font according to those terms in your own work. I am using Android Emoji as a web font here if you're interested.
Worth noting too is the Phantom Emoji project which is creating an open source set of full colour emoji.
Emoji are just fancy emoticons, and last I checked, emoticons aren't generally protected by copyright (because of their small size; to my knowledge, you normally can't copyright individual words, which is what emoticons/emoji are equivalent to. You can trademark them, though). However, I doubt they could be properly trademarked, either, considering their generic nature/common usage. A logo/etc. that contains emoji could probably be trademarked (and it's almost certain that at least one has, though I can't think of any off the top of my head), but I don't believe the emoji itself could.
At the very least, you're as likely to encounter legal trouble when using emoji as you are when quoting an internet meme.
If you are using these from font then no, but if you copied these to your project resources - add notice to your about window. If you want to use them on Windows (from Mac to Windows) you must.