PhpOffice\PhpPresentation\Shape\Drawing\Base64::getMimeType PHP Method

    public function getMimeType()
    {
        $sImage = $this->getContents();
        if (!function_exists('getimagesizefromstring')) {
            $uri = 'data://application/octet-stream;base64,' . base64_encode($sImage);
            $image = getimagesize($uri);
        } else {
            $image = getimagesizefromstring($sImage);
        }
        return image_type_to_mime_type($image[2]);
    }

 public function testMimeType()
 {
     $oDrawing = new Base64();
     $oDrawing->setData($this->imageData);
     $this->assertEquals('image/jpeg', $oDrawing->getMimeType());
 }