[Mimedefang] Image blocking idea

[WBrown at e1b.org]

Here's an idea for blocking image spam:  What about taking the idea of 
SURBL and DNSRBls and extending it to images.  My proposal is to hash the 
image and do a DNS query using the hash value and domain hosting the image 
RBL.

This eliminates the need to OCR the graphic, and if they obscure the text, 
it doesn't matter. If they send the same image to many recipients, it'll 
get detected blocked.

Maybe combine this with OCR, doing the hash/lookup first since it should 
be low cpu cost (but slow on network lookup unless it's already cached). 
Odds of a false positive would depend on hash length which would really 
only be limited by the RFCs for DNS.  How long can any element of a DNS 
name be?  Total length of a fully qualified name?

A collegue suggested calling such a system Gerbil, taking the sound of the 
last 5 letter of "image RBL".

---

"Solving the spam problem is like curing cancer. It's not one disease but 
100 diseases, each with their own issues."  -- John Levine co-chairman of 
the independent Antispam Research Group, part of the Internet Engineering 
Task Force.


William Brown
Web Development & Messaging Services
Technology Services, WNYRIC, Erie 1 BOCES
(716)821-7285