I don't think the person who went outside of the room for the group photo is clearly visible on one of your photos, so I don't expect there to be a practical problem with the photos that's you posted.

On the other hand going forward I would want to have a system that allows people to clearly signal that the don't want to have photos taken of themselves.

From the LessWrong regulars, if gwern would attend a meetup I would guess that he would be uncomfortable with photos of him afterwards being available online.

While being a toastmaster I remember having a board member of my local toastmasters club who didn't want picture of him on the internet because he had a public persona as a musician and didn't want the information of being in a toastmasters club associated with that persona.