The only way to check it is through server side upload component.

Date:  Thu, 18 Jan 2001 16:36:13 -0000
Author:  "Balasubramaniam. R" <mailbala@c...>
Subject:  File validation
 
In a page I browse for some files to upload files. Once the files are
selected for uploading, I need to perform a validation that whether those
files are really present in the client machine. Because there is a
possibility that the user might have keyed in some junk text or a file
which is not there. Now I perform this validation in the server side which
I feel is not proper way to do the same.. Do help.
regards,
bala