Ah, that’s one of the easier ways to do it! You can just use a text widget.
Upload the image onto your server somewhere. Or if it already somewhere, note the URL.
Drag a text widget into your sidebar, and use this code
If you want the badge to link somewhere if clicked, the code is
<a href="https://www.clicklink.com">
<img src="https://www.yoursite.com/image" alt="title" />
</a>
if you don’t want it to link anywhere, and just want an image, use just the second line from that to display the image
clicklink= link you want people to go to if they click the image
yoursite.com/image needs to be swapped out for the URL to your actual image