The flaw was spotted by Spanish phone expert MarcianoTech, who was testing the Galaxy S8 at its official launch in New York, USA. The phones expert was actually live on Periscope when he first tricked the S8 with a photo of himself, shown via another device. Experts believe the same flaw may also be the same problem on the S7 S8+ model, which has a fingerprint sensor and iris scanner. Samsung launched the phone with many new security features, such as an iris sensor and fingerprint sensor, including a fingerprint scanner.
Source: https://www.bleepingcomputer.com/news/mobile/you-can-bypass-facial-recognition-on-new-samsung-galaxy-s8-phones-using-a-photo/