The easiest and quickest way we have found to batch resize all of our eBay photos to meet eBay’s new picture size requirements is by using a free tool called Picture Resizer 6.0 which can be downloaded for free here: http://www.rw-designer.com/picture-resize
The new eBay size requirements are that your photos are at least 500 megapixels on the longest side.
This tool allows you to drag and drop entire picture folders into it and have all of the pictures resized at once. We were able to resize our entire picture library with over 50,000 photos within an hour!
You can also customize what size you want your images to be, whether or not to overwrite the existing photos, and you can even have the images sharpened at the same time!
After the pictures have been resized you can upload them into your existing eBay listings or use them for any of your new eBay listings.