distribution box

Q: Outside the Madrasah bookshop there are some boxes of old/used kitaabs on a bench. Some people put their kitaabs which they don't want in the boxes. Other peoples kitaabs end up in the box without them knowing, e.g. someone misplaced his kitaab and someone else put it in the boxes. Also at the beginning of the term /year kitaabs which weren't claimed are put in the boxes by other people not by the owner. Is it permissible to take kitaabs from the boxes? If kitaabs were taken must it be put back?