Does it need the internet?
No. The countdown and the blink check both run on your phone. Nothing is uploaded and there is no account.
Can it see my other photos?
No. GroupCam asks for the camera only. It saves its own shots to your gallery in a GroupCam album and never reads your photo library.
What happens if someone blinks?
The photo is checked right after it is taken. If a blink is found, GroupCam says so and takes one more shot. It retakes once, not repeatedly, so a session cannot get stuck.
How does it know a face blinked?
It looks at each face in the full-resolution photo and reads how open each eye is. Faces too small to judge are left alone rather than triggering a retake, so someone at the back of a group will not cause an unnecessary reshoot.
Is the blink check perfect?
No, and the app does not claim it is. Each photo is labelled with how many faces were checked and whether blinks were found, so you can see what it actually looked at.
How loud is it?
Loud enough for a room. You set the session volume in Settings, and if your phone has no speech engine it falls back to a chime with an on-screen countdown.
Do I pay again later?
No. It is $4.99 once.