The portraits are 400x400 in <drive>:\Program Files (x86)\Steam\steamapps\common\Torment Tides of Numenera\WIN\TidesOfNumenera_Data\StreamingAssets\assetbundles\Player
The images are called
Portrait-LCO_Female
Portrait-LCO_Male
(you need an asset viewer to see them, they are inside the Player file)
1. Get the Unity Asset Bundle Extractor tool (UABE)