How to choose the Chinese captcha code

How to choose Chinese verification code?
The English verification code is used to define 26 uppercase and lowercase alphanumeric array random subscript to obtain a random verification code
How can I get a random Chinese verification code? Is it not too big to define an array of Chinese as in English?

------Solution--------------------
Note that the UCS-2 encoding of Chinese characters is continuous from 0x4e00 to 0x9fa6.
So you just
$ch = Iconv (' ucs-2 ', ' Utf-8 ', pack (' n ', rand (0x4e00, 0X9FA6)));
You can randomly get a Chinese character


------Solution--------------------
Build a common font, and the verification function does not need to enumerate all characters commonly used

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