QuickLook and Spotlight plugins to display the dimensions, size and DPI of an image in the title bar instead of the filename. Also preview some unsupported formats like WebP & bpg.
It doesn't work for me either. I'm on the same Mojave version. The plugin is listed when I run qlmanage -m, but no image dimensions when previewing images in quicklook.
Does it work on macOS 10.14.5 (18F132)? I'm running latest qlImageSize (2.6.1). There's no info shown for any image.