Thanks for tinysoft now my code is working well.

Qt Code: 
  1. void Dialog::RetrieveFromDatabase()
  2. {
  3.     QString imagePath = QFileDialog::getSaveFileName(this,"Save image to",QDir::currentPath(),"JPEG Image (*.jpg)");
  4.     QModelIndex index;
  6.     QByteArray bytes;
  7.  
  8.     QSqlQuery query;
  9.     query.prepare("SELECT image FROM `test`.`images` WHERE `id_no`=:id;");
  10.     query.bindValue(":id",ui->lineID->text());
  11.     if (!query.exec())
  12.     {
  13.         QMessageBox::critical(this,"Query error",query.lastError().text());
  14.     }
  15.     else
  16.     {
  17.         //Set model
  18.         model.setQuery(query);
  19.         index = model.index(0,0);
  20.         bytes = index.data().toByteArray();
  21.  
  22.         //Save image
  23.         QImage imageWrite;
  24.         imageWrite.loadFromData(bytes);
  25.         imageWrite.save(imagePath,"JPG");
  26.  
  27.     }
  28. }
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