A trend has been detected: people taking digital photos of projected images during a talk at a conference or departmental seminar. I have some colleagues who do this, and I always wonder what they do with all those photos. In these cases, the colleagues are not trying to steal anyone's data or ideas, they just want to have a record of the talks they go to (according to them, this is better than notes in a notebook). In other cases, the motivation of the photographer may be more nefarious..
I personally would never take a photo of someone else's talk. If I see an image that I desperately want to have or look at more, I would ask the speaker later, explaining the reason for my interest and what my likely use would be of such an image. I have only done this once or twice to get a cool image for teaching.
If someone takes a photo during one of my talks, I don't really mind but I think it is kind of rude and distracting.
1 year ago