Dr Tromer's method recognises this fingerprint by comparing it with a pre-assembled library of such prints that a snooper has made from videos the viewership of which he might want to follow.

特拉能够识别出这指纹，方法是把它和预先建的视频指纹库进行比——监测人员已经预先他们想要跟踪收视情况的影片提取了指纹。