There is also a video posted on iDeviceHelp channel, proving what we are actually asking. The Galaxy S8 can be easily fooled by just showing him a picture from the user of the device who locked the phone. You can see the video right below.
Besides the Google’s Face Unlock, which was easy to compromise, Samsung released their own interpretation of the feature. That includes that the feature requires blinking with your eyes before unlocking. This all happened back in 2012, but now the company seem to have forgotten that feature.
Even that system though, from 2012, can be easily fooled by using two photos, one of the person with opened eyes, and other with the eyes closed. If you are skilled enough, you can switch between the photos faster, and unlock the device. The feature is still plausible to be done on the Galaxy S8 as well.
So, as a conclusion, we should not take the facial recognition system from the Galaxy S8 as much of a secure thing for our device.