php生成圖形驗證碼

<?php

session_start();
// main
$vcodes = '';
//generate Number 4
srand((double) microtime() * 1000000);
for ($i = 0; $i < 4; $i++) {
    $vcodes .= rand(1, 9);
}
$_SESSION['eifr_checkvcode'] = $vcodes;
if (function_exists('imagecreate')) {
    //generate picture validation code
    Header("Content-type: image/PNG");
    $img = imagecreate(44, 18);
    $bg  = ImageColorAllocate($img, 245, 245, 245);
    imagefill($img, 0, 0, $bg); //background

//generate Number 4
for ($i = 0; $i < 4; $i++) {
    $font = ImageColorAllocate($img, rand(100, 255), rand(0, 100), rand(100, 255));
    $vnum = substr($vcodes, $i, 1);
    imagestring($img, 5, 2 + $i * 10, 1, $vnum, $font);
}
//add interference
for ($i = 0; $i < 100; $i++) {
    $randcolor = ImageColorallocate($img, rand(0, 255), rand(0, 255), rand(0, 255));
    imagesetpixel($img, rand() % 70, rand() % 30, $randcolor);
}
ImagePNG($img);
ImageDestroy($img);

}
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