In short, this theory is my own defense on why images on computer and LCD screen look better on dark background. This is where I found my images posted on Flickr and forums to look different from the same ones I posted on my photoblog.
Photography nowadays comes in 2 flavors: print and electric display (including lightbox display and slides). In the traditional form of print, the perception of imagery relies on ambient light source (such as sunlight) to reflect the image on the print to the eyes. For electronic display the need for ambient light becomes unnecessary as light of the LCD screen and slide projector substitute ambient light.
Now, how does this have to do with the choice of background color?
As light source already exists within the area of the image itself, any additional area of brightness on the screen wouldn’t be needed. This is why we always see lightbox advertisement or art display (for example, Jeff Wall) filling the whole lightbox as any white border will lessen the impact of the primary image. Seeing an electronic image on white background would be like seeing printed image while holding it up to the sun. Too much light from too many sources.
This is why dark background works. Dark area represent the edge of the lightbox that gives the image its full potential for visual impact as it helps our eyes to focus on the image.
Anyway, this is just another of my passing thoughts. I may have to revise this theory again.