// [1] 图片不重复，可自由缩放
    ui->label->setStyleSheet("QLabel{"
                             "border-image:url(:/images/bd.png) 4 4 4 4 stretch stretch;"
                             "}");

    // [2] 图片不重复，大小固定
    ui->label_2->setStyleSheet("QLabel{"
                               "background-image:url(:/images/bd.png);"
                               "background-position:top right;"
                               "background-origin:content;"
                               "background-repeat:none;"
                               "}");

    // [3] 图片不重复，可设置缩放比例，不可动态缩放
    QImage* img = new QImage;
    img->load(QString(":/images/bd.png"));
    QImage scaledimg;
    scaledimg = img->scaled(ui->label_3->width(),ui->label_3->height(),Qt::KeepAspectRatio);
    ui->label_3->setPixmap(QPixmap::fromImage(scaledimg));