如何初始化图片“；blob”；在PHP构造函数中键入

我有一个类，我想初始化存储类型为"blob"的pictuer的列，但我不确定如何初始化？看一下代码的最后一行

  public function __construct( $data=array() ) {
    if ( isset( $data['id'] ) ) $this->id = (int) $data['id'];
    if ( isset( $data['date'] ) ) $this->date= (int) $data['date'];
    if ( isset( $data['topic'] ) ) $this->topic = preg_replace ( "/[^'.','-'_'''"'@'?'!':'$ a-zA-Z0-9()]/", "", $data['topic'] );
    if ( isset( $data['author'] ) ) $this->author = preg_replace ( "/[^'.','-'_'''"'@'?'!':'$ a-zA-Z0-9()]/", "", $data['author'] );
    if ( isset( $data['content'] ) ) $this->content = $data['content'];
    if ( isset( $data['picture'] ) ) $this->picture ="Here sholud be the Type" $data['picture'];
  }