Open a save as window for a .jpeg

Is it possible to open a save as windows from flash to download a jpeg? At the moment I can download a zip file using the following code, but when I change the extension to .jpg it opens up a new browser window showing the image.

function onMouse1Click(evt:MouseEvent){
    var request:URLRequest = new URLRequest("images/SPR.zip");
    navigateToURL(request);
}
download_btn.addEventListener(MouseEvent.CLICK, onMouse1Click);

Cheers :beer: