That is specific for this implementation. Note that cursive/handwritten text will continue to be an issue, but machine printed is pretty solid and especially easy if you can narrow down the scope of the expected result (somewhere in this thread someone wonders of it would be possible to prefer 0 to o etc - sure). Note that

a) it's not possible to consistently reach 100% (and depending on the source material and circumstances far less) recognition (have to educate customers about that..)

b) errors are a tradeoff between 'dunno' and 'might be a zero' aka miss vs. false positive. Benchmarks/evaluations usually consider the latter far worse, prefering jf?oster to jf0ster by a long shot. So that's what you'll try to archive.

Source: Approaching ten years (yeah..) in a company that sells OCR solutions and more, integrating Abby, Oce and another half a dozen commercial engines.