href image link download on click

<a download="custom-filename.jpg" href="/path/to/image" title="ImageName">
    <img alt="ImageName" src="/path/to/image">
</a>

It's not yet fully supported caniuse, but you can use with modernizr (under Non-core detects) to check the support of the browser.

The easiest way of creating download link for image or html is setting download attribute, but this solution works in modern browsers only.

<a href="/path/to/image" download="myimage"><img src="/path/to/image" /></a>

"myimage" is a name of file to download. Extension will be added automatically Example here

<a href="download.php?file=path/<?=$row['file_name']?>">Download</a>

download.php:

<?php

$file = $_GET['file'];

download_file($file);

function download_file( $fullPath ){

  // Must be fresh start
  if( headers_sent() )
    die('Headers Sent');

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

  // File Exists?
  if( file_exists($fullPath) ){

    // Parse Info / Get Extension
    $fsize = filesize($fullPath);
    $path_parts = pathinfo($fullPath);
    $ext = strtolower($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/vnd.ms-excel"; break;
      case "ppt": $ctype="application/vnd.ms-powerpoint"; 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";
    }

    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: $ctype");
    header("Content-Disposition: attachment; filename=\"".basename($fullPath)."\";" );
    header("Content-Transfer-Encoding: binary");
    header("Content-Length: ".$fsize);
    ob_clean();
    flush();
    readfile( $fullPath );

  } else
    die('File Not Found');

}
?>

If you are Using HTML5 you can add the attribute 'download' to your links.

<a href="/test.pdf" download>

http://www.w3schools.com/tags/att_a_download.asp