Oscars JPEG Thumb Maker
Oscars's JPEG Thumb-Maker helps creating small thumbnail pictures of your images. While it may look complex, it isn't. What you need is to choose source directory of JPEGs, optionally with all subdirectories and then the output directory. Set the desired Width and Height and various options and go - press Start. The software will always take care to protect the aspect ratio of the images, no matter what. While you set some desired size, some images could not be perfectly resized to it since their ratio may be different. For example if the source is 1600x1200 then the image may be perfectly resized to 640x480 without anything else since both have the same W/H ratio. However if your desired size would be 600x400 then such image can't be resized without changing the ratio - which we don't want.