how do i make users to download jpg files

i need to make users download jpg files. i know that if i send them the link to the jpg file, the browser will just display the jpg file. Then the user must do rightclick -> s开发者_JS百科ave picture as

However, i want to force the download dialog box to appear so that they can download the jpg file. Anyone can help me with that?

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You need to set the correct headers in your PHP script that serves the image to the user

header("Cache-Control: public");
header("Content-Description: File Transfer");
header("Content-Disposition: attachment; filename=$file");
header("Content-Type: image/jpg");
header("Content-Transfer-Encoding: binary");

//read image, write to user