[Prakticant]

Actually, I'd like to calculate how many people we are able to portrait at once (i.e. your graduate class of '15) and still recognize them.
I assume the people faces may take up to 1/8 of the photograph.
It means we have 24/8 = 3 MPix for people faces.
I estimate we need around 0.07MPix for a woman/man face to be recognized by small densely pixel-packed sensor (all that difraction, lens resolution, shake, DoF, etc. accounted).
The above means we could portrait up to 42 people at once with our K-3, for our decendants
If your class is bigger than 42, employ 645 , Fuji, or make panorama shot

[Imp]

huh? My class picture has 250 people in them, all recognizable