Manual:$wgCopyUploadsFromSpecialUpload

Details
By default, upload by URL, when enabled via $wgAllowCopyUploads, is only possible using the API (or extensions such as UploadWizard). To make the option usable from Special:Upload, you can set this variable to true.

In order to make use of this option, users also need to have the option $wgAllowCopyUploads set to true and the associated user right.

Example usage
This example setup will allow all autoconfirmed users to upload by URL, via Special:Upload or the API. Add to the bottom of your LocalSettings.php:

See slso

 * $wgAllowCopyUploads