The POS UI in AX can be customised in many ways and one of the more dramatic ones are changes in the background images. The steps are few and goes like this:
Open the Images form
Create the images in the Images table. In this case we create two. This may vary in your situation
Open the Visual profiles form
Create a visual profile and add the images here
Create a register and device and add the visual profile to the register
To get this running on the POS you need to distribute data. Job 1090 should be sufficient. When the data is applied you are ready to enjoy the results:
This is just the basics of what you can do, but I hope you get the idea of what is possible.