Ah, so it's not dynamic then. That makes it easier and actually possible with pure macros. I'd recommend uploading the image to your location of choice (roll20 library, imgur, whatever you like as long as the url will end in .jpg, .png, or .gif - depending on the image type). You can then pull the image into chat using the markdown format: [Image Description](<a href="https://someImage.jpg" rel="nofollow">https://someImage.jpg</a>). You could of course set this as a macro, or even embed them in a query in a macro to select which one you want.