Baldur's Gate

I will just post the stuff from the answer. You make the images in any image program. Even MS Paint should be able to do it.

Custom Portraits

The measurements for player portraits are 38X60 pixels for the small ones
(8-bit color only) and 110X170 pixels for the large ones. Put these in
the Portraits directory (in the install directory for the game) and add a
S to the end of the small portrait name and an L to the end of the large
portrait. The names must be 1-7 letters long, maximum.
For example:
XXXXXXXS.bmp for small (38x60, 8-bit)
XXXXXXXL.bmp for large (110x70, 24-bit)
For multiplayer, each player must have a copy of the portraits, otherwise they will
see a blank icon where the other player's custom portraits would be.