I agree with both the comments below in that the experimental data provided on the results was minimal.

Along these same lines, I am curious how well their algorithm fits the actual usage of an image retrieval system. For example, the paper presents applications of the algorithm to extract classes of images from a set of diverse images. They seem to brush under the rug the idea of searching a more homogeneous database, or with a more homogeneous set of input (i.e. a specific type of car, a specific flower or the Eifel tower). I would be curious to see how well the algorithm responds to changes in the database and queries.

This seems to get at the larger point that the paper should have layed out more definative goals. Even though the paper states that there is currently not a definative set of tests, the paper could attempt to formulate a set of experiments that would confirm that the goals that the algorithm was designed for were accomplished.

On a side note, I found the layout of the last few figures a bit interesting. Was I the only one that was slightly confused to find the last two figures after the references?