Hello @kartik,
You can also do this via curl, just you need a path to an image file and pass it to the function given below..
public static function getImageDataFromUrl($url)
{
    $urlParts = pathinfo($url);
    $extension = $urlParts['extension'];
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_HEADER, 0);
    $response = curl_exec($ch);
    curl_close($ch);
    $base64 = 'data:image/' . $extension . ';base64,' . base64_encode($response);
    return $base64;
}
Thank You!!