One of my distributors provided me a full catalog export in CSV format including product images. I have thousands of products that have been uploaded into the product database. But the included image files are not in the *.jpg *_i.jpg *_t.jpg file structure needed by AC7. Manually uploading every product image file one-by-one is not an option.
All product image files were named matching the SKU value of each product and in GIF format.

There are several image batch resizer utilities available on the internet. I reviewed a few and went with one from

For $20, I have resized thousands of product images into the the standard size, thumbnail size and icon size. The program also lets you automatically tack on the _i or _t suffix as needed. Every image was converted on the fly into JPG format. A watermark could be automatically added to every image however I elected not to do so. Time to convert all three sizes in my computer was about 10 minutes.
The program supports converting several different formats into a common output format, so your source pictures don't even need to all be the same format.  It also has a handy feature called "Canvas Resize" that helps ALOT when dealing with source images that vary wildly in size.
Tech support has been very responsive and friendly – typically you find one or the other but both is rare.

By converting the images to the proper size, JPG format and required file naming convention, I just moved the converted files into the ~/Assets/ProductImages folder of my AC7 site. All store products immediately pick up the files thanks to the checkbox in the Images admin screen.   Absolutely no effort involved in AC7 to attach the images to the correct products.