Hello,
it appears that the thumbnail is created according to the max height and max width settings in the plugin. So if I have those at, say, 400x300 pixels the thumbnails will be generated at that size. If I later change the setting to 640x480 pixels, the thumbnails are not resized, so they still display at 400x300 pixels.
I think there should be an option to resize the thumbnails, otherwise the width and height settings has no influence on existing images.
Furthermore, when I install the plugin all existing images (that have been attached with the wpforo standard attachment feature) are displayed very large. Probably because no thumbnails exist for those - but it would be nice to have the option to display images as large as that with the plugin installed as well. Is that possible at all?