Do both methods require a photograph of the fingerprint or eye? Seems to me it would be much easier to surreptitiously snap a photo of someone's face and eye than their fingerprint.
Maybe. People often rest their hands on a table. That's how Starbug (the same guy who originally faked Touch Id) later took a photo of a thumb from six feet away and created a duplicate. The person wasn't aware.
OTOH, someone aiming directly at your eyes means they're in your direct eyeshot.
In either case, though, few would think their identity was being stolen.
Also, as kids and pranksters have shown, it's easy to use a sleeping person's finger to unlock their phone. Prying open their eyes is more likely to wake them up
Take a random person like me for example - there are hundreds of photos of my face (including my eyes) floating around in the internet.
But
how many taken in infrared mode, which is how this fake was done (iris scanners use a flood of IR instead of visible light).
One the other hand, there are exactly zero photos of my fingers (let alone fingerprints) anywhere.
Really, no pics of you waving hello, making a peace sign, thumbs up, etc?
More importantly, fingers leave prints. (Starbug's original demo lifted one off the phone itself.). Looking at your phone does not leave an iris image
Samsung Iris recognition is a gimmick at best. And not even a good gimmick.
Like everyone else, Samsung uses iris recognition tech from a third party company.
As noted, just as with fingerprint recognition, biometric implementations in smartphones so far have been more about speed than actual security. I.e. waiting for blinks, pulses, etc would annoy most users. And could usually be easily faked, anyway.
Biometrics alone is not secure. Worse, once stolen, you can't easily change yours. But it's convenient and "good enough" for mass consumer use.