After activating the plugin it goes to work. Look at your frontend to see what happens. If you have a lot of smaller images than set in "Article, Blog, Category, Featured settings" width and height in for instance article and featured, you'd better set "Thumbnail size allow big than max size images" and "Crop image (Zoom Crop)" to "No".
Having set that it looks just great. Clicking on the generated thumbnail on the frontend gives the orignal image in a Lightbox. Very cool. Kudoos Denys!