Stands to override (instead of using the one from the game).
To override one, you need to place a png named <character>.png, where <character> is the name of the character in the game's files.
Notable differences are:
- Reisen, named "udonge"
- Cirno, named "chirno"
- Meiling, named "meirin"
Otherwise, it's pretty much what you'd expect the value to be (Reimu is reimu, Marisa is marisa, ...)
To change the alignment, go in characterPortraits.css and modify the left to move it left and right, and bottom to move it up and down

These can also be overriden manually using OBS's custom CSS rules