I never understood the concept of a background image on my screen. Most of the time, I have applications open which block me from seeing it. If i DO need to see it, I want to see the icons, and any image just makes it harder to see/read them.
My 'image' is just solid black, so all the icons "pop" off the screen, and are easy to read.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors
I am like Bear, I don't use desktop icons unless temporarily as a clipboard, so visibility does not matter to me there, and when I have windows open they cover the background anyway. I can't do solid colors I look at that all day at work, I like having something a little less blah on my home PC. I will agree that many backgrounds are to busy and can hurt the eyes after awhile though.
I usually use some space related desktop background because when I close or minimize everything that is what I see and calms me a lot. And sometimes I use some quotes on my desktop to make me get bak to work and stop wasting my time with pointless things.