Before we start

There are just two minor points left before we can start coding.

Do you have ImageMagick?

ImageMagick should be installed on your system before you can use it in your scripts. This means you will either have to install it yourself, or have your server admin do it for you.

If your server is running PHP in safe mode, which it is likely to be if you're using a (free) shared host, your scripts don't have the right to execute shell commands. As this script runs ImageMagick as a shell command, you won't be able to use it. You could a. ask your hosting provider to disable safe mode or b. use the GD library to generate your images. ImageMagick is far more powerful than the GD library, but you can use the latter even in safe mode.

Why write your own script?

Directly running convert isn't the only way to use ImageMagick in your scripts. The Imagick module from the PEAR library, PerlMagick, a Perl interface to ImageMagick, can do this too. Then why bother and write your own script? Because it gives you a far more flexible system. You just enter your commands as the query string, and the script just sends them to ImageMagick. The PEAR module, for instance, has a special PHP function for each ImageMagick command. The script would have to translate the commands to the corresponding functions, for which it would need an array with all possible commands and functions. The direct method, withouth PEAR module, is therefore faster to write.