PHP验证码函数的示例，当然，这只是一种实现方式，有需要的朋友可以参考。
代码如下：
function _code($_code_length = 4, $_width = 75, $_height = 25){ for($i=0;$i<$_code_length;$i++){ $_nmsg .= dechex(mt_rand(0,15)); } $_SESSION["code"] = $_nmsg; $_img = imagecreatetruecolor($_width, $_height); $_white = imagecolorallocate($_img, 250, 250, 250); imagefill($_img, 0, 0, $_white); $_gray = imagecolorallocate($_img, 196, 196, 196); imagerectangle($_img, 0, 0, $_width-1, $_height-1, $_gray); for ($i=0; $i < 6; $i++) { $_md_color = imagecolorallocate($_img, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255)); imageline($_img, mt_rand(0,$_width), mt_rand(0, $_height),mt_rand(0,$_width), mt_rand(0, $_height), $_md_color); } for ($i=0; $i < 50; $i++) { $_md_color = imagecolorallocate($_img, mt_rand(200,255), mt_rand(200,255), mt_rand(200,255)); imagestring($_img, 1, mt_rand(1,$_width-5), mt_rand(1, $_height-5), "*", $_md_color); } for ($i=0; $i < $_code_length ; $i++) { $_md_color = imagecolorallocate($_img, mt_rand(0,102), mt_rand(0,102), mt_rand(0,102)); imagestring($_img, 5, $i * $_width/$_code_length+ mt_rand(1, 10), mt_rand(1, $_height/2), $_SESSION["code"][$i], $_md_color); } header("Content-Type:image/png"); imagepng($_img); imagedestroy($_img); }