I kind of doubt that copyright would cover board positions or puzzles themselves which are board positions. It might cover how they’re presented, the diagram order, the accompanying text/commentary etc. I’m sure josekipedia would’ve run into some similar issue years ago if although maybe there’s just no point in trying to get a position/sequence removed from a joseki explorer.
In any case, I wouldn’t plan on transcribing the whole books. Some are about joseki in the context of fuseki which don’t suit the explorer here (not going to set up whole board positions). It also wouldn’t be useful to add any analysis to a sequence if it contained multiple mistakes (which some books do if they’re reviewing amateur players games like MJ books mentioned above).
The two main problems are just how time consuming it is, and how strong your evaluation of the positions are to really judge if something is even or good/bad for one side etc. I imagine this gets very hard to do in the avalanche, taisha, that magic sword joseki or some of the complicated 3-3 ones.