If you have windows, you can use
Ant Renamer 2.10. It can make random names and is very easy to use. Drag & drop your images in the program, click 'Actions', 'Random Name', and 'Go' and you're done.
There's other random file name generators (just google 'random file name' and you'll get stuff), but I already had Ant on my computer since it's a great overall batch file renamer.