Probability of given position/piece configuration I'm currently working on an image based FEN generator. I found a paper doing the same and they have used Stockfish to  calculate  the  most probable piece configurations.
Now I wonder if Stockfish has this functionality or if they implemented it on their own. Does anybody know more about this, as it would be extremely helpful for my project?

On pages 7-8, the paper gives information on what they did.

Utilizing a chess engine: We utilized the open-source Stockfish engine, which  allows us to calculate the most probable piece configurations. By calculating the prob-abilities of all possible configurations, we could choose the most probable candidate (see Figure 7). Additionally, we strengthened this method by utilizing large-scale chess game statistics in the manner proposed by Acher and Es-nault Acher and Esnault (2016).
Utilizing a chess engine: We utilized the open-source Stockfish engine, which allows us to calculate the most probable piece configurations. By calculating the prob-abilities of all possible configurations, we could choose the most probable candidate (see Figure 7). Additionally, we strengthened this method by utilizing large-scale chess game statistics in the manner proposed by Acher and Es-nault Acher and Esnault (2016).

This makes literally no sense to me- SF is just an engine, and can't exactly give stats on most probable piece configs, and even if the researchers wrote some code to do such, it would be different than the most probable ones in human play.
My suggestion would be to use CQL on some database and search for each configuration.
Alternatively, SCIDvsPC (free) and ChessBase (paid, and quite expensive) can search for these sort of configurations as well, so you might want to use those.
As for what database to use, my recommendation would be Caissabase (free)