I created three folders on my hard drive: thumbs, medium and large and marked the medium files _MED and large _LRG.

In my web-host's control panel (C-panel) I have a folder
"www. ..../store/admin/images/"
that includes folders "LARGE" and "MEDIUM" (those folders are populated with ZEN Cart template images of merchandise).

I tried uploading my images into those two folders and the images show up in my "product description page" and "larger image" pop-up window.

Now, here is the problem:
When I upload _MED image into MEDIUM folder, the image in both the MEDIUM and LARGE folders is medium size, and that is what is displayed in "product description page" and "larger image" pop-up window.
As soon as I upload a _LRG image into LARGE folder, the image in MEDIUM is replaced by the _LRG image.
If I re-upload the _MED image into MEDIUM folder, the _LRG image in the LARGE folder is replaced my a _MED image.
It keeps me running in circles.

What's up? Am I using a wrong folder/directory for uploads?

BTW, this is a problem, as I did not want to transform my Large image into a regular square the way I did my MED images. So where MEd size should go (product description) I get a very blurry, distorted image.