Why PHP Verification code cannot be displayed

Some time ago, when debugging the program, the verification code can not open the situation,

First of all make sure you have opened the GD library! As long as you are not the lower version of PHP basically this is the default! Just add the following code to test it first!

If you don't look for another reason!

The final result of the test is that the Ob_clean () must be used before outputting the captcha image.

This function is used to discard the contents of the output buffer, if your site has many generated picture class files, then you want to access the correct, you should always clear the buffer.

Why PHP Verification code cannot be displayed