Best place to start...
http://www.pioneerelectronics.com/StaticFiles/Manuals/Car/AVH-P4400BH_OwnersManual051712.pdf
Page 74 for installation of background, and if you read through it will tell you display sizes of images to use.
Just joined, my first background for the x940bt installed in my MKiii Supra...
[URL=http://s755.photobucket.com/user/Drake1969/media/My%20Whip/BackgroundMK3_zpse2b8e6e2.jpg.html][/URL]