Maybe i did not explain myself clearly, i apologize for that, english is not my first language. i will attemp to walk you through the process to see if you can understand it.
when creating HTML newsletters, we create HTML code that refers the image (HREF) to a link on a website, at the same time, the image itself is on a web site (SRC), and what people see in their email, is a reference of this image in a server.
when we create this html, there is a line that reads (in this example):
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