Add in ASP simple CAPTCHA to prevent automatic bot submission

Hello, We have a form that bots are using to submit thousands of requests through POSTs. We want to add a check which would ensure bots do not auto-submit the form. This is in Classic ASP on Windows 2012 R2 server IIS 8. Attached are the files related to the POST requests: 2017-01-24 16:24:01 W3SVC118 flash [login to view URL] POST /[login to view URL] - 80 - 5.188.211.15 HTTP/1.1 Mozilla/4.0+(compatible;+MSIE+6.0;+Windows+NT+5.1;+SV1) ASPSESSIONIDSATSBDAA=DJHHALHDLPCCADDKBEPGBABC [login to view URL] [login to view URL] 302 0 0 420 2090 140 REQUIREMENT: ============= - Complete in 3 days or less - Code must be secure and optimized to work quickly - simple CAPTCHA (nothing complicated, just something easy for clients to use) - Code must be in ASP [login to view URL]: The file on the website that is visible which has the Submit button [login to view URL]: This is the file being POST into causing the spam issue [login to view URL]: The file related to the one above that sends the emails To qualify for this project, you must answer the two questions below: 1. Which CAPTCHA or verification technology you'll be using 2. Which files you'll need to edit to fix this problem