Image size java script needed please

Hi. I don't know if you can help but I need a java script but can not find one like I need. I have images, usually about 100X100 pixels automatically uploaded to my site. They are supposed to be thumb size but sometimes the user submits a fuill size image. Is there a way to have it look at the size of the image submitted, see if its is too large and then use a different jpg that I know will be a thumbnail size? Or use that jpg if it is less than say 120 pixels wide. Sort of like max-width.

Any help would be appreciated
Thanks
JoeImage size java script neede dplease

i think that you really need a server side language for this. javascript would be able to ( with some difficulty ) figure out after the file is uploaded, if it's the right size. but, i think in general. you could set up a much better system with a server side language.