protected function getPreviewImageSource()
    {
        $imageName = $this->getViewFileName('jpg');
    
        $reflector = new \ReflectionClass($this);
        $dirPath = dirname($reflector->getFileName(), 2);
        $imagePath = $dirPath . '/images/blocks/' . $imageName;
        // file get content resolved Yii aliases.
        $data = FileHelper::getFileContent($imagePath);
        if ($data) {
            return 'data:image/jpg;base64,' . base64_encode($data);
        }
        
        return false;
    }