Fingerprint scanner placement on Samsung Galaxy S8 was a last second decision
Low yields during production of the 10nm chipsets that are going into the phone (the Snapdragon 835 or the Exynos 8895 depending on the region where you purchase the handset) have already delayed the unveiling of the phone by several weeks, and the launch of the phone by one full week. Sammy simply did not have the time to make sure that Synaptics' in-display biometric reader was working perfectly.
In fact, according to an anonymous source close to the situation, Samsung threw money at the in-display fingerprint reader, but was getting frustrated with the results. While some Samsung fans could be let down by the ultimate placement of the scanner (users could easily smudge the camera by mistake), the tenth anniversary Apple iPhone 8 could have its Touch ID fingerprint scanner placed under the front glass. According to super Apple analyst Ming-Chi Kuo of KGI Securities, there is also talk that Apple will be forced to use a "revolutionary" new front-facing camera that uses face recognition to unlock the phone or to verify identification. That could be a sign that Apple is experiencing trouble with an in-display fingerprint reader as well.
Samsung will also turn to face recognition due to an iris scanner that apparently runs too slowly. But this works to a Galaxy S8 owner's advantage. Using a user's facial features on the Galaxy S8 will reportedly unlock the handset in .01 seconds.
source: KoreaTimes via SlashGear