Block DDOS attack on a particular file?

It appears that my server is the target of a moderate DDOS attack from IP addresses in Brazil. I've implemented mod_evasive, which is doing a good job of identifying the attack requests, but the rate of rotation of the IPs is too great for mod_evasive to be of any real assistance.

The good news is that the DDOS attack is focused on requests for a couple of very specific .jpg files (which do not exist, of course).

I'm running apf.

Is there a way to configure my firewall to block http requests for these specific files, and/or to block only those IPs that request these specific files?

Thanks in advance for your help and ideas.