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.
Late last year, there was some speculation that the Samsung Galaxy S5 would launch with a retina scanner, which obviously was not meant to be. But perhaps it will be found on the Samsung Galaxy Note 4, which is expected to be unveiled in September, at IFA 2014 in Berlin.
source: @SamsungExynos via Ubergizmo