Seems that I was searching in the wrong directory.
Imageveux creates the thumbs in the same folder as where it places the uploaded images. Wasn't expecting that. Problem solved, thanks again for the tip!
Would it be possible to have a little pane in the config for a specific photo where you can "drag" the thumbnail around, so you can "aim" the crop? That would be fantastic.
Yea, it would be cool ... Many of you photographers are understandably picky about the motive of your thumbnails, and some thumbs need to be created manually. We will look into it!