Welcome to the Discourse community! The question has come up a few times, but it’s a legitimate issue. You can find details about the issue here: Fix broken images for posts created by the WP Discourse and RSS plugins. Details about the cause of the issue are in my first reply to that topic.
If possible, the best approach for dealing with the issue is to add the domain(s) that the images are being downloaded from to your Discourse disabled image download domains site setting. This will prevent Discourse from attempting to download the images. It is the process of downloading the remote images that causes them to break.
To fix the issue with existing posts that have broken images, edit the post to add an empty line above the markdown tag that has been created for the image. For example, if you see markup that looks like this:
<p></p>
edit the post to change it to:
<p>
</p>