Reloading Images Using JavaScript
There are some situations where you want to reload an image without refreshing the page containing it. This is especially handy with CAPTCHA images, where you might want to give the user the option to get a new code in case the first is too hard to read.
It sounds simple enough, but then there is browser caching that you need to work around. Fortunately, this problem is easy to solve just by altering the URL of the source, adding a unique string to the end (such as a timestamp) as a GET parameter. Here is a little JavaScript function that will accomplish this:
Creating a CAPTCHA in PHP with GD
A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a system designed to test if input is originating from a human or a computer. The most common method, which you have probably seen, is displaying an image containing distorted text and asking the user to type in the text. It is difficult for a computer to read it and relatively easy for humans, so it is assumed that a correct answer must have originated from a human. This is a tool used to prevent automated spam.
Anyway, this tutorial will explain how to make your own CAPTCHA like the one below using PHP and the bundled GD image manipulation library. This is the method I use on many projects, and it does the job. Keep in mind that there are stronger CAPTCHA systems available if you want to block the more motivated spammers.
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