Hi @Mackenzie Miller ,
I just tried testing in my Exchange 2019 lab environment with the html code below, the image(I used the image you shared above in the post.) can show properly in Outlook 2019 desktop client:
<IMG src="/api/attachments/145871-image.png"?platform=QnA alt="Contoso logo">
Would you mind have a check and see if you are using the same <IMG> tag to point to the image available on the Internet? Or you can remove all personal information involved, including the image url, then share a snippet of the html code you used, and I'll see if I can reproduce the issue using your code.
Besides, it's recommended to have a go on one of the Outlook desktop clients, go to File > Options > Trust Center > Trust Center Settings > Automatic Download, clear the checkbox of "Don't download pictures automatically in standar HTML email messages or RSS items"and see if it can be of some help:
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