As we know that the term CAPTCHA (for Completely Automated Public Turing Test To Tell Computers and Humans Apart) was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University.
It is a program that protects websites against bots by asking a user to complete a simple test which humans can pass but most of the current computer programs cannot. Most common type of CAPTCHA requires that the user type letters or digits from a distorted image that appears on the screen. Like the one seen below.
So, as we can understand that CAPTHCHA is used for preventing bots and not for testing eyesight of the user. Hence a 4 digit number written in extremely small fonts with (style="font-style:oblique; font-family:Geneva, Arial, Helvetica, sans-serif) does not help. The keyword here is IMAGE.
Also, disabling right click is not a very smart move and will be of no use if the CAPTCHA is in plain text format.
The current system may not you help in ensuring that your registration service is not being misused. Image will not appears, unless it is coded hence allowing images in browser will also not be of much help here :)
For more information and free CAPTCHA please click here.