How to acquire file_exists in AS3?

programming flash
1

Hi!

I’m making huge map using tiles. There is a lot of white tiles so I would like to optimize it deleting them from server and make a if statment. Something like file_exists from PHP:
if (there is no file with name 1-2-24.jpg) {
addWhiteRect();
}
Is it possible in AS3? Not to try loading the file and use 404 as my solution (I think it is not to good for server, am I right?)?

Regards
Taurus76