If you are used to using Composer, adding PHP extensions to a Heroku PHP app is really easy. For adding the GD library, just add the extension as follows to the “require” section of your project’s composer.json file:
"require":
{
"ext-gd": "*",
"laravel/framework": "4.1.28",
"doctrine/dbal": "2.4.2",
"guzzlehttp/guzzle": "4.0.2",
"way/generators": "2.6",
"fzaninotto/faker": "v1.3.0"
},
Heroku has a complete list of already included extensions and those available to be added during deployment.