State the name of the object class that has in most images.
object class that has in most images refers to OBJ_CLASS where MAX(COUNT(OBJ_CLASS_ID));
SELECT OBJ_CLASS FROM IMG_OBJ AS T1 INNER JOIN OBJ_CLASSES AS T2 ON T1.OBJ_CLASS_ID = T2.OBJ_CLASS_ID GROUP BY T2.OBJ_CLASS ORDER BY COUNT(T1.OBJ_CLASS_ID) DESC LIMIT 1