I was wondering how the Hi-Tech Camera 4 stack ability works.

"When skills cause damage to units, units get extra 1*power points in damage"

What is considered a skill and does this trigger off every damage tick?

This makes sense for the autocast magic abilities like Marissa's laser beam and should trigger with each tick of damage. However, do passive skills which launch projectiles or do additional damage benefit from this trigger?

For example:
Do auto attack procs like Remiu's [Spirit Sign] or [Fantasy Nature] trigger the camera damage?
Do auto attack modifier passives such as Koishi's [Rose Hell] trigger the camera damage?
Do poison ticks from Yoshika count as skill damage and trigger the camera damage?