List all the ID of the images that have an attribute class of "horse".
ID of all images refer to IMG_ID; attribute class of "horse" refers to ATT_CLASS = 'horse';
SELECT T2.IMG_ID FROM ATT_CLASSES AS T1 INNER JOIN IMG_OBJ_ATT AS T2 ON T1.ATT_CLASS_ID = T2.ATT_CLASS_ID WHERE T1.ATT_CLASS = 'horse'
database name:db_id image_and_language
ATT_CLASSES table ATT_CLASSES Cols: ATTRIBUTE CLASS ID dtype integer, ATTRIBUTE CLASS dtype text, 
OBJ_CLASSES table OBJ_CLASSES Cols: OBJECT CLASS ID dtype integer, OBJECT CLASS dtype text, 
IMG_OBJ table IMG_OBJ Cols: IMAGE ID dtype integer, OBJECT SAMPLE ID dtype integer, OBJECT CLASS ID dtype integer, X dtype integer, Y dtype integer, W dtype integer, H dtype integer, 
IMG_OBJ_ATT table IMG_OBJ_ATT Cols: IMAGE ID dtype integer, ATTRIBUTE CLASS ID dtype integer, OBJECT SAMPLE ID dtype integer, 
PRED_CLASSES table PRED_CLASSES Cols: PREDICTION CLASS ID dtype integer, PREDICTION CLASS dtype text, 
IMG_REL table IMG_REL Cols: IMAGE ID dtype integer, PREDICTION CLASS ID dtype integer, OBJECT1 SAMPLE ID dtype integer, OBJECT2 SAMPLE ID dtype integer, 
