How to solve the problem that php cannot display the verification code image

Solution to the problem that php cannot display the verification code image: 1. Remove the semicolon in ";extension=php_gd2.dll"; 2. Change the encoding format of the code to a BOM-free format; 3. Use "ob_clean ()" function clears the cache.

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Question

##Today, I created a new virtual host locally and deployed a small php website that I wrote before. Because I used the wamp integrated environment before, this situation did not occur. Now I suddenly find that the verification code cannot be generated.

So I started my journey to find bugs. I searched for many solutions on the Internet and finally solved it. Now I share it as follows:

bug1

When the above situation occurs, the final solution is A basic mistake is that you probably forget to install the gd module in php.

In the window environment, you only need to find it in the php.ini file

;extension=php_gd2.dll

Just remove the semicolon in front of it. After restarting apache, you can find this in phpinfo()

If you are under the ubuntu environment, you need to install the gd module. The command is

sudo apt-get install php5-gd

After installation, you can also see the above module.

bug2

If you find that it still doesn’t work after the above installation, then it may be the following problem

Your code is probably using something like If edited with a text editor such as editpuls or notepad, their default encoding format is utf-8 with BOM.

UTF-8 BOM is also called UTF-8 signature. In fact, UTF-8 BOM has no effect on UFT-8. It is added to support UTF-16 and UTF-32

BOM, BOM signature means to tell the editor what encoding the current file uses to facilitate the editor's identification, but although the BOM is in the editor

## It will not be displayed, but output will be generated, just like an extra blank line.

Generally I use UTF-8 BOM-free format
So you need to change the encoding format of the code to

BOM-free format.

bug3

#If you go through the above two steps and find that it still doesn’t work, then you have to use your trump card.

Use ob_clean() and clear the cache.

ob_clean This function is used to discard the contents of the output buffer. If you have many generated image files, then if you want to access them correctly, you must Clear the buffer frequently.

	public function create()
	{
		ob_clean();
		$a = new verify();
		session::set('captcha', strtolower($a->create(4, 15)));
		view::assign("captcha", $a);
		view::display("captcha");
		exit(0);
	}

Now, everyone can see that it is back to normal

Note: If you use higher php version, then undefined variables cannot be used, otherwise a

notice error will be reported. $new_number and $_SESSION['check_checks'] must be judged with isset before use or you use old code If so, add error_reporting(E_ALL) at the beginning & ~E_NOTICE); shields notice errors (not recommended), so use isset() to make sure it is defined. Otherwise, the verification code may not be displayed.

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