What can be done about a DDoS attack?

[annotate]

I have a person or bot that keeps requesting an image(s) that exists on my website creating multiple 404s. I can't block the image because other users might request it. Sometimes over a period of time I might get 2000 emails about 404s. He doesn't do it real fast, just continually and it doesn't create a big load on my server. He changes IPs constantly and changes images that he requests as well so I can't block his IPs. He's in the process of doing it right now and has been for over 24 hours. What can I do with CSF? Thanks for any help.

Also, when I get a 404 I receive an email from my server. This is how I know when he is attacking.

[zemanelcenas]

If doesn't create a big load or issue for your server or service then provably the only real DDoS is the annoying emails you are reviving. If you publish content on the internet it is normal at same point the content being indexed by search engines and other bots.

You should try to understand better what is happening, for what are you saying it can actually be legit traffic.