The Indian Railways runs one of the largest ecommerce sites in India - a site that has seen a consistent YoY growth over the last few years since its launched. Last year, they are believed to have earned a revenue of nearly 100M USD.
The guys who built their reservation system have very good engineering chops - in fact these systems hit peak load of about a million queries (every day) during 10 AM - 12 noon (IST) when users and reservation agents try to access the site irctc.co.in from browsers / mobile / reservation counters etc.
The "captcha" was not even in this page a month back. The "PNR Enquiry" for which this page is intended is a feature that can be accessed through SMS & also from the irctc website. This is possibly the least visited page in indianrail.gov.in
I have been an active user of both irctc.co.in & indianrail.gov.in over the last 7-8 years and have seen how these sites have grown.