My company had a team event and we have several group photos (with 10-20 people in them). Some colleagues were not there so now I have a task to take their individual photos and to insert them into the group photos (i.e. to replace some of existing people's faces with those ones). What would be the best way to do it? How to take the individual photos, what should I pay attention to, what's the best way to make light and colors same as in the original photos...?
This assumes you have at least basic photography & Photoshop skills, and access to the same or at least ball-park similar quality camera to that the master shot was done on. If we're talking about phone photos, all bets are off.
To get the best start, you want to be in the same location with the same lighting as the original photo. Stand the replacements in the same places as those they're replacing, keep the camera at the same distance & direction as the master shot [set focus by re-framing, if necessary]. Same lens isn't vital, but will save resizing later.
This will give you basic matching for lighting & perspective. Perspective is even more important than lighting. If you can't match light you might be able to airbrush. If you can't match perspective it won't work.
If you can shoot tethered, set up an arrangement whereby you can quickly flip between the master shot & the proposed replacement.
If the background on the master shot was anything other than plain, then add in a plain backdrop for the new shots, to make cutting the subjects easier.
This doesn't mean you have no hill to climb, but it does make the slope shallower.