Two similar questions were recently sent o Rav Yitzchak Zilbershtein, rav of the Ramat Elchonon neighborhood of Bnei Braq.

In the first, an avreich walks every Shabbos from Bnei Braq to Givatayim to give a shiur torah to a group of people. The walk is two hours long, so he is very dedicated in his attempt at bringing Torah to a secular/traditional crowd and possibly bring them closer to religious Judaism!

In the second question, a Hassidic woman who gives a shiur on Shabbos in a secular neighborhood had the same issue and question.

The avreich weekly encounters a parent of one of the young men in his shiur who lies in wait along the route, snaps a picture of the avreich and then sends the picture out on a local Whatsapp group warning people to stay away from, and keep their kids away from, this missionary.

The Hassidic woman also encounters a woman who snaps her photograph and sends it out warning others about the taliban woman who comes to the neighborhood.

The questions presented were, are they allowed to smile for the camera? The avreich asked the question suggesting that perhaps if he looks friendly rather than dour, people receiving the picture will be less afraid of him and will perhaps even increase the number of attendees in the shiur. The Hassidic woman said she smiles for the camera and each week at least one additional woman attends the shiur - so is that ok?

After debating the issue and weighing arguments to both allow it and prohibit it, Rav Zilbershtein paskened that they should smile for the camera so as to teach the father and other woman to not bother as it wont help, similar to the rule by wine when a goy touches the wine intentionally and we make an exception allowing the Jew to drink that wine so as to deter the goy from doing this.
source: Kikar