These letters in a distorted image available on the login page are called CAPTCHA and is a latest security enhancement feature in internet logins.
A CAPTCHA is a program that generates and grades various simple tests that humans can pass but automated computer programs cannot. For example, humans can read distorted images, but automated computer programs cannot. Hence, this helps in ensuring better security for internet based transactions.
The term CAPTCHA (based upon the word “capture”) is a contrived acronym for Completely Automated Public Turing test to tell Computers and Humans Apart. This was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University.