Re: Taking still images from phantom 2 w/H3-D3 and GoPro 3+B
you are correct that since you don't have wifi control of the device (you do NOT want to fly with wifi on!) to start recording anything you need to press the button before takeoff... I'd recommend pressing it before you turn on the propellers
The GoPro is capable of taking stills and video at the same time "Simultaneous Photo and Video mode" however there are some restrictions, see the chart below for which video resolutions yield which photo results:
I'm not intimately familiar with this settings, but many people around here say the still you get in photo+video mode aren't quite the same quality you get in the photo-only modes, so alternately you could just put the gopro in time lapse photo-only mode, have it taking a photo every 1, 2, 5 etc seconds.
If you have a live FPV system on your Phantom there are some quirks: I can confirm personally in Photo+Video mode the video feed "blanks" briefly (half a second maybe) when the gopro take a picture. so if you have your photos every 2 seconds you'll get a blackout every 2 seconds, it's kind of annoying so I had it take a photo every 5 seconds and it was more manageable.
I can NOT confirm people are saying live FPV video does not work at all in photo-only mode so that's a bummer if true. I hope to test that out in the next few days