Slow image processing

First off, thanks for a great plugin. But there’s an issue I am trying to figure out for quite a while:
– When I upload several images in a form, they upload;
– But it takes way too long (30sec or more) for a thumbnail to show up
– And only afterwards it proceeds to the second image, and so on.

I honestly don’t have any ideas what slows the process down…

The page I need help with: [log in to see the link]