State the object class of the image with tallest bounding box.
bounding box refers to X, Y, W, H from IMG_OBJ; tallest relates to the height of the bounding box which refers to MAX(H); object class refers to OBJ_CLASS;
SELECT T2.OBJ_CLASS FROM IMG_OBJ AS T1 INNER JOIN OBJ_CLASSES AS T2 ON T1.OBJ_CLASS_ID = T2.OBJ_CLASS_ID ORDER BY T1.H DESC LIMIT 1