Replace the File located here:
Resolution must be 800×481. SCP or use USB stick to overwrite.
The following .png image is transparent. If you have Photoshop or Gimp, you can open this file, and then create a new layer to test backgrounds and see what they will look like on your infotainment screen. There is also a Photoshop .psd file included below.
Click the Image for Full Size - Then Save or Drag to Desktop
Original Infotainment Background:
Click the following link to download the .psd file (Note: the .png transparency above would be easier) http://mazda3revolution.com/forums/attachment.php?attachmentid=79914&d=1409797471
Click Image to Save: