I am a photographer. We have around 30 people who do not allow us to take a photo of them during an institute for 4 weeks. Around 600 will attend and apparently it is not easy to follow the permission.How can I handle this situation? Please help me. Thanks for your advice in advance.
I'd have expected the organizers to have permission to photograph and video from all the attendees, typically done as part of the terms and conditions of agreeing to attend.
I'd suggest contacting the organizers and finding out what arrangements and terms and conditions are in place. You should probably ask them to seek cooperation from the attendees.
If it's a minority that refuse to cooperate, I'd use the suggestion by @eric-shain and color code the name tags (of those who object). I wouldn't be surprised if they'd object to be color coded as well, but at least ask the organizers. :-)
It's unusual to have people at conferences refuse to be photographed (or videoed). This is especially pointless now that everyone and his mother has a phone that can do video and still and those people rarely ask permission to do so (or use the material later).
Ask them to take a photo of them with their name to be able to remove the photos after the conference is done.
Have a release paper explaining what and how you will do it.
You will have a list of private photos of people that you know you can remove (or blur out) from your global photo pool.
Carry with you a supply of cheap self-stick neon-colored dots (3/4 to 1" diameter, typically sold at office supply stores or hardware stores to price items at garage sales). If someone doesn't want their photo taken at the conference, give them a neon dot to stick on their name tag or near their face (on their chest or shoulder) so you can blur them out.