The background is a classroom、blackboard、ceiling、machine

nsfw, lowres, bad anatomy, bad proportions, bad hands, bad perspective, text, error, missing fingers, extra digit, extra arms, extra legs, fewer digits, cropped, worst quality, low quality, normal quality, jpeg artifacts, signature, watermark, sample watermark, username, blurry, white background, ((from side)), from below, from above, from behind, wide shot, far away, very wide shot, (head out of frame), out of frame, holding,