The Galaxy S8 won't come with a physical home button and thus needs a new and awkward location for the fingerprint sensor. But it's not as if Samsung didn't try to integrate the sensor into the screen.
Samsung apparently had hopes of bundling a fingerprint sensor directly in the Galaxy S8's display, creating a new feature technology that would have separated the device from competitors. However, after trying out the feature with supplier Synaptics, Samsung found that the process was slow and the results "frustrating," according to a report from The Investor that was earlier reported on by Sammobile.
According to the report, Samsung had hoped that Synaptics' technology, which relies upon technology baked into the glass to scan a fingerprint, would ultimately deliver a reliable alternative to physical fingerprint sensors. However, the company decided that the technology was still too new and apparently not reliable enough to find its way to the device.
Meanwhile, the iPhone 8 is rumored to include Touch ID technology directly into its display, and Apple has applied for a number of patents related to this type of design. Apple's device may also include a front 3D camera for facial recognition. The Investor report says that "Apple’s possible adoption of on-screen fingerprint scanning for the new iPhone 8 could steal the show from Samsung."
Samsung ultimately decided at the last minute to bundle a physical fingerprint sensor in the device and place it in a wonky spot at the back of the handset next to the rear-facing camera, at least according to the latest leaked images of the final design.
Based on all of the Galaxy S8 rumors, the device nixes the physical home button on the front to make room for a larger screen and smaller bezel. The company has been criticized, however, for placing a fingerprint sensor on the back directly next to the rear-facing camera. Some believe that the move could ultimately cause smudging of the lens.
Other devices, like the new LG G6, offer back-mounted fingerprint sensors that are placed below the rear-facing lens, safely away from the camera.