Thumbnails and medium versions of the images will all be resized in HTML from a large (775px X 1000px) JPEG.
:: detour to put on 'user' hat ::
Nooooooo! Keeping only one version of each file in your database is fine. But any resizing needs to be done server-side. Otherwise the site will be seen as inexplicably slow-loading. This is not only a human-interface issue; search engines measure page access time too. Your server can resize an image in much less time than it takes a human to download the oversized version.