imagecreatetruecolor() returns an image identifier representing a black image of the specified size.
Depending on your PHP and GD versions this function is defined or not. With PHP 4.0.6 through 4.1.x this function always exists if the GD module is loaded, but calling it without GD2 being installed PHP will issue a fatal error and exit. With PHP 4.2.x this behaviour is different in issuing a warning instead of an error. Other versions only define this function, if the correct GD version is installed.
Example 1. Creating a new GD image stream and outputting an image.
The above example will output something similar to:
Note: This function requires GD 2.0.1 or later (2.0.28 or later is recommended).
Note: This function will not work with GIF file formats.