Change image file size dynamically

Hi Group, Is there any way to change the image size (Not height and width. I am talking about image file size) dynamically? Our users upload the big files and we want to find a way so once user upload such file, system will automatically generate the small file and store both versions on the server location. Later on this small file will show up as the thumbnail. Once user clicks on thumbnail then system will show the original big file. Thanks Hardik ----- Hardik K. Doshi Web Application Developer Institute of Design Illinois Institute of Technology 350, North Lasalle Street Chicago, Illinois 60610 312.595.4907 (direct) 312.595.4901 (fax) __________________________________ Do you Yahoo!? SBC Yahoo! DSL - Now only $29.95 per month! http://sbc.yahoo.com