If you didn’t know it was available, once you’ve saved a character scroll to the bottom of the character edit screen and you’ll see a portrait URL input box. Type in a proper URL that points to an image and it will show up on the Character List screen (see attached screenshot).
If the sheet you are using has an actual portrait field on the sheet (right now the only one that has this is the Mouse Guard sheet) then when you fill in your portrait URL and save your character it will display the portrait on your character sheet.
Cthulhu Mythos has always fascinated me. Crazy cultists and great Old Ones vying for power while insignificant humans struggle to prevent the world from devolving into a chaotic, evil mess all while battling their own slowly deteriorating mind.
I’ll dispense with the Fate fanboy comments and point you to that Fate Character Sheet website that I run. This is a place to store your Fate characters and Adversaries. This has both Fate Core and Fate Accelerated characters sheets and other settings that I love. It’s free, so tell your friends and start storing your Fate roleplaying stuff on my site!