The images for the products is located at :
/product_images/ folder
Exactly :

/product_images = the image with original size
/product_images/thumbnails/150x150 = the resized image to 150x150
/product_images/thumbnails/100x100 = the resized image to 100x100
/product_images/thumbnails/90x90 = the resized image to 90x90
/product_images/thumbnails/70x70 = the resized image to 70x70

If you upload the image using the admin section the image uploading
and resizing to this formats.

If you not happy with the rezulted images quality, possible to upload
the image using ftp to this folders.

OK so it is a bug then that it is not creating these images automatically. They are not being created from the upload tool accessed from the "Choose" option of the item. Any recommendation how to fix it?

I post for you in a mail the changed image upload function

OK I'll be looking for that mail message. Thanks.

Is a recomendation only. If you not like the shop image upload function
(the result of the resize) possible to use the described method.

It's not that I don't like it. It does not work. It only uploads the image. It does not produce the resized images at all.