The de-facto bot prevention technique sprawls everywhere on the web but I am surprised how people overestimate the difficulty of breaking a captcha. Here are some of them which I encountered.
convert captcha.jpg -threshold 5% a.jpg
Adjust the threshold value to get a binary image with no noise.
tesseract -l eng a.jpg text
This will create a “text.txt” file with the captcha text in it.
I ran a test on effectiveness of these commands and the success rate was nearly 9 / 10, clearly implying how weak or better say, made-from-scratch captcha implementations are as good as having none at all.