With the advent of mobile phones and tablets, I see this happening more and more: People taking photos of the slides during a presentation.
Why do they do that? And is that a good thing or a bad thing?
A good thing would be if your slide says something insightful and they want to share it on a social network. A bad thing would be if your slide contains too much text and they want to capture it because they're overwhelmed.
And then there's people like me, who take photos of slides as examples - good or bad - since they teach others about presenting. But we are probably a minority in your audience.
I have a suspicion that the majority of people who take photos of slides during a presentation do so as a replacement for taking notes. Another aspect is a certain feeling of guilt with regards to the topic: It gives them the feeling that they're doing something about it.
What I mean by this: At conferences, the slides are usually made available afterwards. But that can often take several days, if not weeks, and I think some people in the audience feel that a) the need to have the information available pretty much immediately and b) know that they probably won't really look at the slides once they're available.
It's a sign of our fast-moving times: We are aware of the importance of the topic right now, during the presentation. When the slides become available, next week or so, however, we are already busy with something else. We may actually download the slides, but we never really look at them; they just end up sitting on our hard drive somewhere.
Taking photos gives us the slides now. And even when we don't look at those photos ever again, it at least gives us the illusion that we did something about the topic of the talk (after all, there's a reason why we attended this specific presentation in the first place).
Assuming your slides are not snapped as bad examples, I don't think there's much you, as a speaker, can - or should! - do about people photographing them. You can try and proactively upload your slides somewhere, so that you can tell your audience where to get them during the talk (near the beginning, so they know they don't have to take photos). That still won't stop some people and, again, it's not something that you should try and suppress.
As a member of the audience, I only like to apply to my fellow attendees: If you take photos, please try to do it discreetly and in a way such that you don't block other people's view. Thank you.
(Photo taken during Greg Law's talk at ACCU 2013 - good quote but a tad too long)
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