You can easily change the background of the Server Status module by going into the module.serverstatus.html file and changing the image src path. Note that you'll need to host the image file on a server or service like imgur, gyazo,...

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<div class="gdp-background-image">
    <!-- Change background image here -->
    <img src="<https://i.gyazo.com/a3b4c6d00c96acb5f0091a62773b2c98.png>" alt="Server Image"/>
</div>
...