how would i make get_file.php show only thumbs?

[bit bit spears]

how would i make get_file.php show only thumbs?

what would i change to do this? i have tried messing with the code, and nothing seems to work. If someone takes off

size= or changes the ?size=039 or whatever to some other text, it automatically resorts to the original image, how would i make it goto only the thumb, so that no one can access the intermediate and fullsize picture?

i wanna do this, because i will be allowing guest access, and will have a synchronized gallery that carries the registered user's gallery's pix.