Few suggestions (processing images really could be better):
- make thumb of first image (not last)
- support two words file name images (for example: picture with name: joomla logo.jpg will not be processed.
- i think that bmp extensions is not supported
- if you add really big image (file size over 3mb) your site is down and you cant open site except you remove that image from article
- you could add image cropping when making thumbnails, so every thumb would be same size (like in smartresize plugin)