The options on this page affect icons and images that can optionally be overlaid on the top of thumbnails.
Overlay film sprockets on videos and animations: Adds film sprockets to the sides of video and animation thumbnails.
Overlay rating stars: Opus will overlay the thumbnail image with stars to indicate its assigned rating (if you have assigned the file a rating, that is). Ratings are assigned using the metadata functions.
Overlay aspect ratio bars: Overlay bars representing each image's aspect ratio. Similar to the Overlay relative dimension bars option, but represents the dimensions of each image relative to each other, rather than to the respective widest and tallest image in the folder. A visual representation of the aspect ratio can help if you're using the "fill (resize and crop)" resize mode, where it can be hard to tell whether an image has been cropped and how much. (If you aren't using that mode, you can obviously see an image's aspect ratio from the thumbnail itself, making the bars redundant except for unusual cases with lots of transparency around the edges.)
Overlay relative dimension bars: Opus will draw small horizontal and vertical bar graphs over the thumbnail to represent the dimensions of that image file relative to the largest image in the current directory. This is particularly useful when you have multiple copies of the same image saved at different resolutions - their thumbnails will ordinarily all look the same, and the bar graphs let you tell at a glance which relative size each file is. This option can also be changed from a button or hotkey using the RELDIMENSIONOVERLAYS argument to the internal Set command.
Overlay thumbnail with file type icon: Opus will display a small icon for the type of file in question in the bottom corner of the thumbnail image (e.g. a JPEG image will have the generic .jpg icon displayed in the corner of the thumbnail).
Hide file type icon if type not registered: With the above option on, the file type icon will not be shown if the file type is not registered. This mostly applies to image files that may have no file extension - Opus is still able to display thumbnails for them as it looks at the file contents to determine their type, but there would be no valid icon registered in the system that could be shown.
Overlay thumbnail with icon overlay (if any): Displays icon overlay images like the arrow for a shortcut file in the bottom-left corner of the thumbnail.