OScommerce thumbnail modification

I require the following to be done on my website An easy way to modify the thumbnails on the site without affecting the actual image file on the site. I understand there are contributions such as GD thumbnailer, php thumbnail generator and on the fly contributions that can do such a task I need someone that understands these progreams and only install the best one. It does not have to be the ones that I have mentioned. My website is [login to view URL] . As you will see some of the thumbnails are not in proportion. I need a method to get these into proportion, such as the ones on site http://www.hotlingeriestore.co.uk. Please only bid if you are an expert with OS commerce and fully understand how to make amendign the thumbnails a quick and easy task. I am of the understanding this is a quick and easy task to carry out, so do not expect to pay a lot, I will wish to continue using you for further projects if all goes well.