That can be done on Ancestry, but not WikiTree as far as I know. You would have to adjust the photo using your own software, cropping the photo for each person.
Alternatively, if you've done that on Ancestry, you might be able to take a screen print of each individual portrait, but I doubt the final resolution would be satisfactory.
Edit: I assumed you wanted an individual profile portrait for each person. If not, just follow the instructions others have provided on this thread.