Can the custom rule be used to rename something with a random hash sort of name?

Greetings, i’m looking at the File Rename on upload, premium features. Do you think one of these rules, perhaps the custom field rule, could be used/manipulated to have the file renamed with a random hash sort of name? I’m running a photo competition where people are using Gravity Forms to fill out their entries as posts, with the media upload field for submitting a jpg as their entry.
I would like it if each photo was named a random string of letters numbers so that judges would not get any clues from the file name who submitted the entry. (other benefits too, but primarily this)
Thanks… J A