How about displaying an identicon, that is rendered from the domain, in the address bar? People might soon learn what the icons of their important sites look like and will easily detect if somebody is trying to phish their bank account.
If you have 1000 distinct images, but a given domain has 5 letters that could each be replaced with any of 3 visually identical Unicode characters, then, well, the chances are very high that there exists a plausible impostor domain with the same image. I don't think this is a very workable approach.
An identicon is a hash value represented as an icon. "facebook.com", for instance, may hash to a red image with a yellow line through it. While you wouldn't remember the icon initially, over time you would – or at least your subconsious would. If you ever visisted a fake-Facebook, you'd immediately notice that something was wrong if the icon suddenly was green with a blue dot in it, for instance.
However, teach users to read domain names! If users do not grasp the general concept, e.g., if the supposed identity is just "example" (possibly with some decoration considered insignificant) and not "example.com", how are they supposed to survive? Domains have been around for more than a quarter of a century, the Internet is actually part of our lives… There is no excuse, and there is no sense in pretending that there was no harm in not understanding the basics. That said, there are real ambiguities that have to be addressed.
FFS, if users cant see that somedomainname.com is different than somedomanname.com how does a randomized image of the domain name based on a hash solve this.
I know of at least one site which users a user selected image in the login screen to thwart phishing attempts. Because its user selected its memorable, I think more so than a password for example. It would be hard for a scammer to spoof as well because they don't know the image the user selected when they created the account.
Unfortunately this would probably be less notable and thus memorable if everyone did it.
Here is the discussion on HN: https://news.ycombinator.com/item?id=17947467