Is there an onclick event or something like it for file input?

[drew10]

I am writing an image upload page. It has file field to browse for images. What I want to do is: after a user browses for a file and before they save it, I want to find the width and height. Therefore, I need some sort of event to fire after the user has browsed for a file. Is there any event built in for this, or can I add a commandName and commandArgument to the file field? Any help would be greatly appreciated!
-drew10

 

[drew10]

I've been thinking...and an onclick event would do nothing. I need to know when the file dialog window has closed. I don't know if this can be done.