php如何使用随机函数rand()生成一个数字验证码?答:image=imagecreatetruecolor(80, 25);imagefill($image, 0, 0, imagecolorallocate($image, 255, 255, 255));for($i=0;$i<4;$i++){ rand_color=imagecolorallocate($image, rand(0,155), rand(0,155), rand(0,155));code_tmp=dechex(rand(1,15));code.=$code_tmp;imagestring($...