PHP generates an image verification code and click to switch to an instance _ PHP Tutorial

PHP generates image verification codes and click to switch instances. Let's take a look at the following results: phpsession_start (); functionrandom ($ len) {$ srcstr1a2s3d4f5g6hj8k9qwertyupzxcvbnm; mt_s:

Now let's take a look at the PHP code.

The code is as follows:

<? Php

Session_start ();
Function random ($ len ){
$ Srcstr = "1a2s3d4f5g6hj8k9qwertyupzxcvbnm ";
Mt_srand ();
$ Strs = "";
For ($ I = 0; $ I <$ len; $ I ++ ){
$ Strs. = $ srcstr [mt_rand (0, 30)];
}
Return $ strs;
}

// Randomly generated string
$ Str = random (4 );

// The image width of the verification code
$ Width = 50;

// Height of the verification code Image
$ Height = 25;

// Declare the image format of the layer to be created
@ Header ("Content-Type: image/png ");

// Create a layer
$ Im = imagecreate ($ width, $ height );

// Background color
$ Back = imagecolorallocate ($ im, 0xFF, 0xFF, 0xFF );

// Blur the vertex color
$ Pix = imagecolorallocate ($ im, 187,230,247 );

// Font color
$ Font = imagecolorallocate ($ im, 41,163,238 );

// Plot the vertices of fuzzy match.
Mt_srand ();
For ($ I = 0; I I <1000; $ I ++ ){
Imagesetpixel ($ im, mt_rand (0, $ width), mt_rand (0, $ height), $ pix );
}

// Output characters
Imagestring ($ im, 5, 7, 5, $ str, $ font );

// Output rectangle
Imagerectangle ($ im, 0, 0, $ width-1, $ height-1, $ font );

// Output image
Imagepng ($ im );

Imagedestroy ($ im );

$ Str = md5 ($ str );

// Select cookie
// SetCookie ("verification", $ str, time () + 7200 ,"/");

// Select Session
$ _ SESSION ["verification"] = $ str;
?>

Next, you just need to call it on the page:

The code is as follows:

If you want to achieve "cannot see clearly? For a different effect, add the following JS to the page.

The code is as follows:

Function changing (){
Document. getElementById ('checkpic '). src = "/images/checkcode. php? "+ Math. random ();
}

Now let's take a look at the PHP code: php session_start (); function random ($ len) {$ srcstr = "1a2s3d4f5g6hj8k9qwertyupzxcvbnm"; mt_s...