if (function_exists('gd_info')) { echo "GD library is installed."; } else { echo "GD library is not installed."; }This code checks the existence of the `gd_info()` function, which is defined by the GD graphics library. If the function exists, it means that the library is loaded and installed. Otherwise, the library is not installed. The package library for this function is the PHP standard library, which is included in most PHP installations.