Here a very short How-To about thumbnail generation with XNview
First you should download the latest version of XNview, a software to view and convert graphic files, really simple to use! Support of more than 400 graphics formats ! It's free, so do not hesitate!
1st: After installation, start the program:
2nd: Select "Convert" from the tools menu
3rd: And add either pictures or whole folders
4th: Define the "output directory"
5th: Click the "advanced options" button
6th: Cick "OK" and start the conversion
You will now have all your pictures duplicated and as thumbnails in the directory you defined.
You might use XNview for whatever you want, this how-to is just to show how fast and easy it is to create thumbnails for Tradebit.com.