Following piece of code lets you force download a file in php

 // Security, it should be a new start
if( headers_sent() )
    die('Headers already sent, please follow the correct way.');

 // Required for some browsers
    ini_set('zlib.output_compression', 'Off');

$file = "/home/somename/myproject/images/img1.jpg";

if (!file_exists($file)) {
    echo "file not found";

$path_parts = pathinfo($file);

$ext = strtolower($path_parts["extension"]);

// Determine Content Type
switch ($ext) {
    case "pdf": $ctype="application/pdf"; break;
    case "exe": $ctype="application/octet-stream"; break;
    case "zip": $ctype="application/zip"; break;
    case "doc": $ctype="application/msword"; break;
    case "xls": $ctype="application/"; break;
    case "ppt": $ctype="application/"; break;
    case "gif": $ctype="image/gif"; break;
    case "png": $ctype="image/png"; break;
    case "jpeg":
    case "jpg": $ctype="image/jpg"; break;
    default: $ctype="application/force-download";

//will be downloaded as "photo.jpg" to users, you can use original name as well.
$downloadName = "photo." . $ext;
$fsize = filesize($file);

header("Pragma: public"); // required
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: private",false); // required for certain browsers
header("Content-Type: $ctype");
header("Content-Disposition: attachment; filename="".$downloadName."";" );
header("Content-Transfer-Encoding: binary");
header("Content-Length: ".$fsize);
readfile( $file );