I've seen this question asked a few times on the #Digital Experience Trailhead topic. If you have a static resource already uploaded to Salesforce, you can simply reference the resource name with the following syntax:

<img src="/sfsites/c/resource/*insertResourceNameHere*"... >

Be sure to replace insertResourceNameHere with the name of your resource! Here is an example of an image output in my trailhead playground.