Image saved to picture but return false

[RyuShai]

i got problem so crazy
first i take picture by camera in qml them store it to image. Then i used graptoimage to save this picture to disk but file it saved in Pictures folder (default folder of ubuntu ) in different name, look like "IMG_00000001.jpg"
here 2 part of code

qml

console.log("grab to image")
            imagePreview.grabToImage(function(result){
                control.cvtImg2Base64(result);
            })

c++

QString MainControl::cvtImg2Base64(QVariant var)
{
    qDebug()<<Q_FUNC_INFO;
    QImage img = qvariant_cast<QImage>(var);
    qDebug()<<img.save("/home/ryu/Pictures/ryu.jpg"); //return false
    QPixmap pix = QPixmap::fromImage(img);
    qDebug()<<pix.save("/home/ryu/Pictures/shai.jpg"); //return false

anyone can explain for me WHY ?

[Nifiro]

https://doc.qt.io/qt-5/qml-qtquick-itemgrabresult.html#image-prop

console.log("grab to image")
            imagePreview.grabToImage(function(result){
                control.cvtImg2Base64(result.image);
            })

QString MainControl::cvtImg2Base64(QImage img)
{
    qDebug()<<Q_FUNC_INFO;
    qDebug()<<img.save("/home/ryu/Pictures/ryu.jpg");
    QPixmap pix = QPixmap::fromImage(img);
    qDebug()<<pix.save("/home/ryu/Pictures/shai.jpg");
}