I am wondering how hard it would be to integrate thumbnail generation into the product addition process when there is a file associated with a product. I know of other sites that have this as a custom feature for their store. Before the file is uploaded, the user is asked if thumbnails should be generated or if they want to upload their own. If thumbnails are generated, the file is uploaded and a list of thumbnails is shown. The user clicks on the thumbnails they want to use and continue on with product setup.
You may contact us with detailed description of your task, we'll estimate it and if you are interested, we will be glad to do such a modification for you.
Best regards, Alt-team