I am not sure what you are suggesting to register. My theme has thumbnails and i can choose which I want to show with the few sizes – thumbnail, medium, large etc. However I am not sure how to this inside of the top rates posts widget. So I guess it should be a part of the code of the plugin, when displaying thumbnails to display the smallest size, since it is showing in the sidebar, which allows for 50×50 or maybe max 150x150px.
