Ah, back to Augmented Reality stuff! For the first paper, I think that focusing on planes is actually a pretty reasonable assumption. The vast majority of the time there will be at least two planes in which a homography can be determined. Anyway, the results are good but it bothers me that they must manually indicate a planar region in the first image of a video sequence. I'm sure that there is a way to automate this so that the planar region can be determined on the fly. By the way, I want to pick people's brains a bit. Can you think of a real life scenario (application) where this technique would break (other than the obvious of a camera facing a flat wall with no texture)?

The second paper is another important paper in the AR world (and I'm glad it is included here). The main thing is that they are able to determine the plane on the fly, but it requires "markers" with the two black polygonal regions that they use (see figure 5 and 14). This is very similar to what the ARToolkit does. So this is contrary to the first paper which was trying to remove markers altogether. Personally, I believe that there is a middle ground where you can determine a planar region automatically without the need for markers. This is currently where research in the AR world is headed.

One more quick thing... For the last paper regarding the epitomes, Shinko and I were wondering what an epitome of a color gradient would look like. Well I ran one through and the results are interesting. I think the result is a good example of how the patches are put together. Anyway, I've put the results up here:

http://www-cse.ucsd.edu/~mclothie/gradient_epitome.jpg