Create a Pull Zone before you start the Laravel CDN integration.

Create the ./app/helpers.php file and update the ./composer.json as follow:

...
"autoload": {
    "classmap": [
      ...
     ],
     ...
     "files": [
         "app/helpers.php"
     ]
},
...

Execute the command composer dump-autoload to dump the autoloader.

Add the following code to your ./app/helpers.php:

<?php

// global CDN link helper function
function cdn( $asset ){

    // Verify if KeyCDN URLs are present in the config file
    if( !Config::get('app.cdn') )
        return asset( $asset );

    // Get file name incl extension and CDN URLs
    $cdns = Config::get('app.cdn');
    $assetName = basename( $asset );

    // Remove query string
    $assetName = explode("?", $assetName);
    $assetName = $assetName[0];

    // Select the CDN URL based on the extension
    foreach( $cdns as $cdn => $types ) {
        if( preg_match('/^.*\.(' . $types . ')$/i', $assetName) )
            return cdnPath($cdn, $asset);
    }

    // In case of no match use the last in the array
    end($cdns);
    return cdnPath( key( $cdns ) , $asset);

}

function cdnPath($cdn, $asset) {
    return  "//" . rtrim($cdn, "/") . "/" . ltrim( $asset, "/");
}
...

The standard asset() function will be called if no CDN URLs are defined in the ./config/app.php config file.

Define the CDN URLs in the ./config/app.php file.

<?php

return [
    /*
    |--------------------------------------------------------------------------
    | Application KeyCDN domains
    |--------------------------------------------------------------------------
    |
    | Specify different domains for your assets.
    |
    */
    'cdn' => array(
            "cdn.keycdn.com" => "css|js|eot|woff|ttf",
            "img.keycdn.com" => "jpg|jpeg|png|gif|svg",
            "all.keycdn.com" => ""
    ),

    ...

Example:

Use the global helper function in your views:

<img src="{{ cdn( "/img/yourImg.png" ) }}" alt="Your Image loaded from KeyCDN" />

Verify the HTML source code if your assets are loading from KeyCDN.