Original avatars for crewmates are not that bad but if you want to have some fun, add immersion or roleplay your favourite franchise follow these steps:
- Start new game, pick the crew with original avatars (in this case you can rename your characters aswell) or load any.
- Open page with crew avatars ("crew selection screen" in case of 'new game')
- Alt+tab your game. Open folder: ...\Steam\steamapps\common\Into the Stars\Nebraska\Content\PublishedUi\images
- Find PNG-image files named "officer_n" (n - numbers from 0 to 19)
- Find avatar of the crew member you want to customize. Open it in any graphic editor. Edit it or replace with any another image/picture/portrait (512x512 px). Save it - overwrite (as PNG format).
- Restart the game. Load savegame. Now the crew member should have new customized avatar.

Easy and obvious, but maybe you can find it usable. For example: create Firefly, Star Trek, Mass Effect, LEXX or Battlestar Galactica crews, add several funny characters or even your little cat.

PS Sorry devs for offline modding of the original game files. Hope you are not angry if players would use the game that way.
Thanks for reading.