Questions about PHP automatic image generation

For the PHP automatic image generation question, I want a PHP source code like this, which is displayed on this website. I don't know if I can do this ?, Why does PHP automatically generate images?
I want a PHP source code that automatically generates images like this.
Something like this








The token I saw on this website.
I don't know if I can do this?


------ Solution --------------------
Put it in your hard disk and select a display.
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$ Imgs_array = array ('imgs/1.jpg ', 'imgs/2.jpg', 'imgs/3.jpg ');
$ Key = mt_rand (0, count ($ imgs_array)-1 );

$ Your_img = $ imgs_array [$ key];
------ Solution --------------------
You can directly connect to gravatar.com. wordpress also uses this avatar.