PHP uses the GD library to draw and generate CAPTCHA images

First make sure that the php.ini setting has not opened GD extension function, test for example

Print_r (Gd_info ());

Assuming there is a printout of the content, such as the following, the GD feature is open:

Array (    [GD Version] = bundled (2.0.34 compatible)    [FreeType support] + 1    [FreeType Linkage] = Wit H FreeType    [t1lib support] + 1    [gif Read support] + 1    [gif Create support] + 1    [JPG support] = > 1    [PNG support] = 1    [WBMP support] + 1    [XPM support] =     [XBM support] + 1    [JIS -mapped Japanese Font Support] =)

The general process of the GD drawing is as follows:

1. Create a canvas resource

2. Create a color brush

3. Drawing

4. Save picture or Output picture

5. Destroying the Memory canvas resource

Test code such as the following:

<?
Phpheader ("Content-type:image/jpeg"); $width = n;   Wide. High $height = n;  $image = Imagecreate ($width, $height); First step: Create a blank image $white = imagecolorallocate ($image, 0, 0, 0);  The first call to Imagecolorallocate () fills the color palette-based image with the background color, which is the image created with Imagecreate (). $green = imagecolorallocate ($image, 0, 255, 0); Step Two: Assign color imageline to the image ($image, 0, +,-A, $green);  The third step: Draw line Imagerectangle ($image, 100,40,300,100, $green);  Draw Rectangle Imagearc ($image, max, 0, N, $green); Draw round imagestring ($image, +, +, "PHP is Niubi honghong!", $green); Write String $str= "abcdefghjklmnpqrstuvwxyz23456789"; $randstr = substr (Str_shuffle ($STR), 0,4); Imagestring ($image, 14, 100 , 260, $RANDSTR, $green); Captcha Imagettftext ($image, 0, $green, './msjhbd. TTF ', "Chinese vsenglish");  Chinese verification//imagejpeg ($image, './test.jpg ');   Save the picture as Test.jpgimagejpeg ($image) under the current path;  Fourth step: Do not add the file name. Direct output to Web page     Imagedestroy ($image);   Fifth step: Destroy, Recycle resources?>

the test tries the pieces such as the following:

Note: GD Library is powerful enough to draw various reports (such as histogram, pie chart, etc.), thumbnails, watermark and stock charts.

Examples of thumbnail functions:

<?phpheader ("Content-type:image/png"); $width =   The original width. High $height =;  $thumb _width = (int) $width/2; $thumb _height = (int) $height/2; $dst = Imagecreate ($thumb _width, $thumb _height); Create a thumbnail drawing cloth $gray = Imagecolorallocate ($DST, +, +); $src = Imagecreatefrompng ('./me.png '); Read the original image//copy the original to the thumbnail canvas imagecopyresampled ($dst, $src, 0, 0, 0, 0, $thumb _width, $thumb _height, $width, $height); Imagepng ($DST, '/me_thumb.png '); Imagedestroy ($DST); Imagedestroy ($SRC);
>

PHP uses the GD library to draw and generate a Captcha picture