Exactly Klaus, that was what I had in mind. I'm doing right now a 360 of a car's interior and I am coding some interactive animated areas, so that you can turn on the stereo, the motor, etc. I do that by placing an image hotspot in front of a cubical pano's face image (both planes parallel) with the "active image" (the one with the stereo on for example) aligned with it so that by tweening the hotspot's alpha it creates the animation. The very big problem is to make the hotspot image to be aligned with the cube image in the background, I do it by typing values in the code for ox="" oy="" and looking close to the image for it's alignment, there is where bilinear interpolation doesn't let me see well the pixels in both images (they see blurry) and makes hard the alignment.
By the way Klaus, it would be nice with Krpano that if I place a hotspot image with: rx="0" ry="0" rz="0" ath="0" atv="0" and scale="1", say, an image parallel to the front cubical image in a cubical pano without any rotation or scaling it's pixel size would match the ones in the background image, right now I've found that for them to match you've to use a value around: scale="0.523", wich is really quite a strange value and also an imprecise one.
Best Regards.