PHP Dynamic Image Tutorial

You can create images on the fly using PHP.

PHP enables you to create dynamic webpages that include generated images using GD library processes. The open-source code library contains several image-building functions, including those for setting colors, fonts and size. The GD library is bundled with PHP, but you can configure it or install a different version using the instructions available at the PHP.net site.

Instructions

1. Open your PHP file using a PHP, text or HTML editor.

2. Type the following code to create your own Captcha or security string image. Take note of the explanatory comments, preceded by slashes (//). Change the function parameter values to modify the image output according to your needs:

   <?php

   function create_image()
   {
   // header indicating the file type is necessary to display the image data
   header("Content-Type: image/jpeg");

   // generate five-character random string for the Captcha
   // $cap variable holds the string to check user input against
   $randnum = md5(rand(0,999));
   $cap = substr($randnum, 20, 5);

   // set image width and height variables
   $w = 80;
   $h = 32;

   // create image resource using width and height
   $image = ImageCreate($w, $h);

   // set colors using rgb numbers
   $white = ImageColorAllocate($image, 255, 255, 255);
   $red = ImageColorAllocate($image, 255, 50, 0);

   // color the box with params: image resource, x, y, color
   ImageFill($image, 0, 0, $red);

   // add white string to box with params: image, font (1-5), x, y, string and color
   ImageString($image, 5, 20, 8, $cap, $white);

   // output generated jpg image
   ImageJpeg($image);

   // clear resources
   ImageDestroy($image);
   }

   // call the function to display the generated image
   create_image();
   exit();

   ?>

3. Save the file and transfer it to your Web server. Type the file URL in a Web browser to test it.

References

• WebCheatSheet: PHP - Dynamic Image Generation

Resources

• PHP: Image Processing and GD
• PHP: Imagecreate
• PHP: Imagestring