Filename prefixes in file_column

I need to add filename prefix to files uploaded by file_column plugin.
instance the image file uploaded by the user is by name ‘foobar.jpg’
I need to prefix this image with a random number(‘23_foobar.jpg’). I
need to
write this prefixed name to database too.
Is there any way to do this ?

Am I missing something very obvious here ?
Please help