This is a fine example of a need gap which may not been addressed considering it as a minor inconvenience, but actually affects large number of people.

This problem is quite often found in websites with codes, especially hash keys or alphanumeric pass codes which needs to be typed manually from websites. This becomes especially cumbersome, when the code needs to be copied correctly in the first attempt & I'm not talking about captchas.

I think a browser add-on which tells whether it is zero or O when highlighted would be simple to implement.

Let's see what others have to say about this need gap.