I have several race cars on one machine (Ferraris, Lamborghinis, Porsches, Vettes, Saleens etc.), all types of WWII combat aircraft on my laptop (200+ wallpapers) and AHII screenshots (about 30) on my gaming machine.
I found a great little program years ago called Wallmaster that lets you load as many wallpapers as you want (limited to 50 in the free version) and will rotate them on a timer, on boot-up or manually, will resize them to fit your desktop, etc. I liked it well enough to pay for the Pro version.
I rotate on boot-up and have new wallpapers daily.