Changed the summary: "images" -> "thumbnails", I think is clearer this way,
initially I tought is about images with a big file size (we have quite a few of
those, contributing to the huge size of the gallery).

Now to a technical description of the problem: those big thumbnails are created
because of a misfeature in the script used to generate them. The target size is
128x128, but is not easy to create this with Inkscape from command line, so the
script is creating images with a width of 128px and proportional height.
Obviously, this will not work well on images where the height il larget than the
width.
In the past the problem was discusses on the list and AFAIK, at least one script
for creating better thumbnails was posted, but probably was not incorporated in
svg_annotate (svg_annotate is the tool used in the release process to generate
thumbnails).

When (if?) migration to ccHost will take places, we will have thumbnails created
by ccHost, so we have to take care ccHost is generating correct thumbnails.

resolved by the introduction of cchost...