The image is obviously showing what appears to be a retina scanner on a phone, and while it doesn't say that we will see this on the Galaxy Note 4, it could be a huge differentiator for the phablet. A retina scanner is also considered to be more secure than a fingerprint scanner. Samsung added the latter to one of its devices for the first time, with the Samsung Galaxy S5. The actual image on the tweet shows how a retina scanner would be useful when it comes to paying bills online. Sure, fingerprint scanners can also be used to verify identity, but there have been ways to defeat it. A retina scanner would be harder to fool.