Wed. October 29, 3:48:03 PM
Hmmm, neat idea. I think you should somehow implement a cache of the thumbnail version - save it in some folder you don't care to browse through - use a format like "[originalfilename]-[width]x[height].[filetype]", then have your resizer script do a 301 redirect to the file URL (if it exists), otherwise, generate the thumbnail and spit it out like it currently does (when the thumbnail doesn't yet exist).
Also, there is a similar trick - use the "lowsrc" attribute, if that isn't deprecated yet.