do you see a button at the top of these e-mails that says (Load Remote Content) ??
if you do, that means a commercial sender has sent you an email with LINKS to the pictures, such as its logo, stored on their web site. Your Friends do not do that.
If the email is SPAM, and you choose to click on the button, TWO things happen:
• the pictures are sent to you to be displayed.
• the company gets notified of your email address, and possibly your IP address as well. Essentially, looking at the pictures in a SPAM e-mail 'rats you out' to spammers. They now know that this is a good e-mail address, and they should send you MUCH MORE at this e-mail address.
More details in this article, selectable by MacOS version at the top. Older versions are similar, but not identical:
Use Mail Privacy Protection on Mac - Apple Support
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