As someone who works with online account access (online banking for example) for many large US financial companies, I can tell you with 100 percent certainty that CAPTCHAs are not overly difficult to overcome. In fact there are many pre-built kits that are available for under $100.
If this is a serious concern, you’re honestly better off looking at things like two factor authentication. It’s MUCH more secure and effective in preventing someone from accessing an account even with a compromised credential.