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Protecting your images from use out of context

If you want to prevent your images from being "hotlinked" from someone else's site ... why not feed them out via a PHP script that checks the referrer? ... If you've arrived at this article via "www.wellho.net", you should see a clean image - and the image is at the url "http://www.wellho.net/demo/doggypic.php". However - if you go to the URL directly, or you access it embedded within another website - you'll see an image with the words "picture only available within web pages at http://www.wellho/net" overlaid onto it.

The script is a simple one:

<?php
header("Content-type: image/jpeg");
if (preg_match('/www\.wellho\.net/',$_SERVER[HTTP_REFERER])) {
  $file = "doginfield.jpg";
} else {
  $file = "dogstolenfromfield.jpg";
}
$stuff = file_get_contents($file);
print $stuff;
?>


... in fact, that's oversimple in the demo (and if you read it, you could find the images directly!!) and you would for a security script locate your .jpg files away from the document root ...
(written 2010-08-29, updated 2010-08-30)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
H117 - Security in PHP
  [4642] A small teaching program - demonstration of principles only - (2016-02-08)
  [3813] Injection Attacks - PHP, SQL, HTML, Javascript - and how to neutralise them - (2012-07-22)
  [3747] An easy way to comply with the new cookie law if your site is well designed - (2012-06-02)
  [3698] How to stop forms on other sites submitting to your scripts - (2012-04-15)
  [3210] Catchable fatal error in PHP ... How to catch, and alternative solutions such as JSON - (2011-03-22)
  [2688] Security considerations in programming - what do we teach? - (2010-03-22)
  [2628] An example of an injection attack using Javascript - (2010-02-08)
  [2025] Injection Attack if register_globals in on - PHP - (2009-02-04)
  [1779] Injection Attacks - avoiding them in your PHP - (2008-08-31)
  [1747] Who is watching you? - (2008-08-10)
  [1694] Defensive coding techniques in PHP? - (2008-07-02)
  [1679] PHP - Sanitised application principles for security and useability - (2008-06-16)
  [1542] Are nasty programs looking for security holes on your server? - (2008-02-17)
  [1482] A story about benchmarking PHP - (2007-12-23)
  [1396] Using PHP to upload images / Store on MySQL database - security questions - (2007-10-19)
  [1387] Error logging to file not browser in PHP - (2007-10-11)
  [1323] Easy handling of errors in PHP - (2007-08-27)
  [1086] Injection attacks - safeguard your PHP scripts - (2007-02-20)
  [1052] Learning to write secure, maintainable PHP - (2007-01-25)
  [947] What is an SQL injection attack? - (2006-11-27)
  [920] A lion in a cage - PHP - (2006-11-10)
  [426] Robust checking of data entered by users - (2005-08-27)
  [345] Spotting a denial of service attack - (2005-06-12)

H309 - PHP - Maps, Graphics and Geographics
  [4655] Image indexer / thumbnail display scripts in PHP - (2016-02-25)
  [4437] Adding a PHP build option, rotating an image based on camera data, and a new look at thumbnails in PHP - (2015-02-22)
  [4365] The changing face of Christmas - (2014-12-26)
  [4178] Where are you? How to write a geosensitive application - (2013-09-18)
  [3817] Fpdf - generating .pdf documents easily from your PHP program - (2012-07-24)
  [3734] QR codes with marketing logos embedded - (2012-05-16)
  [3584] QR codes - graphics images that provide quick phone links - (2012-01-18)
  [3536] UK Mapping Data - and more to come - under government Open Data measures - (2011-12-03)
  [3447] Needle in a haystack - finding the web server overload - (2011-09-18)
  [3211] Computer Graphics in PHP - World (incoming data) to Pixel (screen) conversion - (2011-03-24)
  [3197] Finding and diverting image requests from rogue domains - (2011-03-08)
  [3133] An image from a website that occasionally comes out as hyroglyphics - (2011-01-14)
  [3027] Server logs - drawing a graph of gathered data - (2010-11-03)
  [2729] Uploading a document or image to its own URL via a browser - (2010-04-18)
  [2675] Redirecting to your main domain for correct security keys - (2010-03-13)
  [2583] Reducing image size on digital photos - PHP - (2010-01-17)
  [2390] Dynamic / changing images on your web page - (2009-09-01)
  [2361] Geocoding - converting address to latitude / Longitude with PHP via Google - (2009-08-14)
  [2343] World Flags in your PHP pages - (2009-08-10)
  [1956] Images for Christmas - (2008-12-21)
  [1923] Making it all worthwhile - (2008-12-04)
  [1756] Ever had One of THOSE mornings? - (2008-08-16)
  [1752] Dynamic maps / geographics in PHP - (2008-08-13)
  [1734] All around the world? - (2008-08-03)
  [1724] addslashes v mysql_real_escape_string in PHP - (2008-07-27)
  [1628] Gant charts - drawing them with a PHP script - (2008-05-03)
  [1391] Ordnance Survey Grid Reference to Latitude / Longitude - (2007-10-14)
  [1390] Converting from postal address to latitude / longitude - (2007-10-13)
  [1389] Controlling and labelling Google maps via PHP - (2007-10-13)
  [1194] Drawing hands on a clock face - PHP - (2007-05-19)
  [1104] Drawing dynamic graphs in PHP - (2007-03-09)
  [937] Display an image from a MySQL database in a web page via PHP - (2006-11-22)
  [665] PHP Image viewing application - (2006-04-01)
  [563] Merging pictures using PHP and GD - (2006-01-13)
  [320] Ordnance Survey - using a 'Get a map' - (2005-05-22)


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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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