Please use phrases such as "secretly recorded" and "covertly recorded" when referring to the videos made by anti-abortion activists.
"Undercover" is another useful word. True, it may invoke in some listeners' minds the image of a government spy who has gone under cover, but as an adjective it means "acting or carried out in secret."
We have concluded that "sting" doesn't apply because it is defined as "an elaborate confidence game" or "an elaborately planned operation engaged in by law enforcement agents to entrap criminals." Those don't fit in this context.