Tourist, a picture line is basically a pose...a good time to take a picture!
Dronak, a challenge line is basically where you step forward together in promenade and stop there. (man is standing on his left foot, lady on her left, both are looking forward.) To get in one from, say, a hover telemark: you're hovering out on your left foot at the end of the telemark and lowering. Staying in promenade, step through (forward) on your right foot, then one more step forward on your left (still in promenade), leaving your right toe where it is. Your weight is on your left foot, with your right foot kind of stretched behind you (but keep some flex in the knee). You can then drop into an oversway, rotate her to a throwaway, or shift back to your right foot (stepping slightly into her) for a right side lunge (she would stay in promenade as she steps back to her left, then shape back over to her left when she gets there).
Does that help?