The problem: You want to display all images from different subfolders (subdirectories) in a flat view (instead of having to navigate to each folder).
One solution using IrfanView
- Download, install and run IrfanView.
- Drag and drop the parent folder from Windows Explorer into the IrfanView window, which opens IrfanView Thumbnails.
- Right-click on the parent directory and select “Load thumbs from all subfolders”:
After a few moments, thumbnails for all images from all subfolders will be displayed: