Sorry to ressurect such an old topic, but while researching for an application I came to this code and I am using this logic. Since the link seems to be long gone I decided to compile a C version of this code, maybe it interests some of you.

Also, I increased the number of ROM checksums to get also some 2MB and 4MB images.

https://gist.github.com/sentient06/7303670

Cheers!