- (NSDragOperation)draggingUpdated:(id <NSDraggingInfo>)sender
{
    NSArray *files = [[sender draggingPasteboard] propertyListForType:NSFileNamesPBoardType]
    for (id filename in files)
    {

        if ([[filename pathExtension] isEqualToString:@"jpg"])
        return NSDragOperationCopy
        else
        return NSDragOperationNone
    }


}