I figured out how to add a Depth of Field blur to an image. I also managed to animate one by having an IPO curve for FDist, the focal distance, to that I can shift the focus from one element in the background to one in the foreground.
But now, I am running into some undocumented territory. Select a camera, and in the IPO editor winow / Camera IPO type,
[...] I'll complete this issue tomorrow...