This technique is also referred to as a "Web beacon", "Web bug", or other similar names.

此项技术也称作“Web beacon”、“Web bug”或其他类似的名称。

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After the images are downloaded, a Web beacon notification is sent to the sender of the junk email that informs the sender that the recipient email address is valid.

下载图像后，会向垃圾电子邮件的发件人发送Web信号通知，告知收件人的电子邮件地址是有效的。

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