At academic conferences, attendees are now often taking photos of the ppt slide presentation given by others. Some conference organisers make it clear that taking photo is not allowed for various reasons, including copyright. I would like to ask if this is indeed a copyright issue as the attendee has already paid for registration, and the photos are for personal use only. On the other hand, I would be more than happy for any attendee to take photos during my talk at conferences. Simply, if I worry about any unpublished results or confidential information, I do not include these in my talk.