对于平面的物体,比如照片,操场这一类的,在上面用on,在里面用in
比如: 照片上摞了一张报纸 there's a piece of newspaper on the photo.
照片上有一只狗 There is a dog in the photo.
孩子们在操场上活动 Kids are playing on the playground.
皮箱被埋在操场 the suitcase is berried in/under the playground。通常都用under,用in的很少,但是一定不能用on