I'll be going from Dublin to London on a trip in November. I have recently purchased a high-quality Nikon camera. I'd like to take photos of the start of my journey and not just when I arrive. My friend told me that taking photos itself might be a breach of GDPR. I also plan to post these photos on Flickr.
Another added related question, why is taking photographs not allowed in airports at passport control and in the area where customs officers do secondary inspections?
Your question falls apart in several bits.
First of all, you can start your photo series at home, getting ready for the travel, getting packed, things loaded in the transport that gets you to the airport, the parts of the airport where you can take photos and so on.
You can take photos with other people in them, at least in Ireland and the UK, as long as you do not post them on open platforms. Sharing with people in a way that is not open is mostly not a problem, but if people see your camera (or phone or whatever) and show they do not want to be in the pic, respect that.
There are parts of airports where there are 'no photo' signs. This is to protect people working there and people passing through immigration and those parts of the airports, and you should always respect those signs.
Posting photos online, wherever and whenever taken, is getting more difficult over the years. What is allowed now may be illegal next month or next year.
To be on the safe side, do not post photos with people recognizable on internet unless you know the people and have asked permission to do so.
That way you will not break current and likely not break future laws. What is currently allowed differs per country and is subject to change, so I will not go into details. (See the comments on the other answer for details.)
If you feel the need to take a photo in the secure area of the airports, where there are usually 'no photo' signs, like to document something the officials there do, ask their permission and go by what they allow you. And if they tell you 'private use only' posting on internet is out of it.
In many parts of the airport you can take photos, it has been quite a time since I was in Dublin, but I have taken photos in many other airports and never had troubles finding ones that did not show forbidden subjects or recognizable people.
In most cases there is not a issue with taking photos at airports. Some airports have become tourist attractions in themselves. I personally love planes, and sometimes joke that half the pictures from my vacations are from the airport and plane (i take alot of pictures in the airport).
It should be ok to take pictures except for these cases:
dont try to take pictures of anything that would be considered airline or airport confidential information. Like going behind a check in counter and take a picture of the airline computer screen, or in rooms that say "employees only" or "restricted".
dont let your picture taking get in the way of airport business. Dont go behind barriers, or get in the way of staff, or slow down the process. For example if you get to board a plane by stairs outside, its nice to get a few pictures with the plane, but dont leave the "path" that you are sopost to walk on to the plane, and dont hold up the line for a bunch of pictures. But if you can step to the side, and dont get in the way, they will let you take pictures.
In general, yes, you can take pictures in the airport and of the planes. Security and passport control is a no, and the inside of the plane is probably a no. I have taken pictures so many times, and only one time, in Barbados, a cleaning lady came up to me as i was taking pictures of a American airlines Jet, and she told me "you arnt sopost to take pictures of planes", and without thinking i chuckled a bit but said nicely, "where is the no photos sign?" and she walked away. I think she just didnt like people touching the glass because she has to clean it. Never had a issue in the many busy airports i have been in, taking lots of pictures.
Infact, you can often ask to see the pilot before or after the flight and get a picture in the cockpit too.
Important nuance here: taking photos with people in them might be problematic as pictures can be considered personal data under GDPR
So if you're taking pictures on the street, you have to ask for consent to feature someone in a shot. GDPR does not allow consent to be asked AFTER the photograph is made, only before. You might not have super big issues if people cannot be easily identified in the shot (e.g. they're facing away from you, super far away, etc.), but better to err on the side of the caution if you intend to publish those pictures.
Furthermore, GDPR also establishes "right to be forgotten" so even if someone okayed the picture (or was not very obvious that it was them), if they request their picture to be taken down, you have to comply with it
About taking pictures at passport control and secondary inspection areas, in general, those areas are not classified as public, so you're not subject to the same legal protections for photographing and filming that are granted to public spaces in most jurisdictions.
