Display missing module error for GD when on Media Settings

[simonrcodrington]

When WordPress is installed on a server is ​missing the GD PHP image library, there should be an admin level warning displayed on the Media Settings admin page.

Without the GD module there will be no intermediate image sizes created when images are uploaded in the media library (the media gallery just uses the full image size by default)

​Without Admin Notice

The Media Settings page should display an admin warning / error that tells the user that they're missing that module and without it no intermediate images will be created. The whole page talks about the various images size and without GD none of these settings will be used for anything.

I've created a simple gist that displays an admin notice if the GD library isn't loaded and the current user is on the Media Settings page.

​With Admin Level Notice

​https://gist.github.com/simonrcodrington/be60b6daae0b966a559878c4ba16d9d0

This has come up a few times now where images haven't been created in the media library and no one has known why. Sometimes hosting providers don't include this extension or they are just not loaded. Having an admin level notice here would make sense.

[simonrcodrington]

Admin page without the notice. The page mentions image resizing, but without GD nothing will be resized

[simonrcodrington]

With the admin notice. Displays only on the media settings page

[joemcgill]

Hi @simonrcodrington,

Thanks for the suggestion. I think it would be really helpful to add an admin warning to the media options page if the server doesn't meet the requirements necessary to create thumbnails. One thing that should be considered, though, is that some systems intentionally turn off the ability to generate thumbnails because that process is offloaded to a separate system or service, so we would want to either make this notice dismissible, or think of ways to detect cases where this has been officially disabled so we don't annoy site users with unnecessary alerts.