Here is a screen shot of ThumbFactory viewing the contents of a directory on my computer. The orange and red boxes indicate selected images. Notice the toolbar which pops up over the image which the cursor is currently over indicating the name and dimensions of the image. After selecting the images to thumbnail, pressing the "Create" button will start the thumbnailing.

All created image files will be placed in a directory called "images". The "Expand" button will show the images at full size. This can also be done by double clicking on an image.