If you have product images with variants, this tool will generate a startimage, with one big product and variants as small thumbnails also. Like this
The format can be changed in the *.json file.
Copy one folder with product images in here (like "GB-5009-1" as an example). Order the images by name. The first image in the folder with the required image ending (for example "-1.jpg", see config) will be the big main image, all others the thumbnails. Just click on "start_ebay.bat". A new "output.jpg" will be written.