Disable cache for some images

Question

I generate some images using a PHP lib.

Sometimes the browser does not load the new generated file.

How can I disable cache just for images created dynamica

Answer 1

I know this topic is old, but it ranks very well in Google. I found out that putting this in your header works well;

<meta Http-Equiv="Cache-Control" Content="no-cache">
<meta Http-Equiv="Pragma" Content="no-cache">
<meta Http-Equiv="Expires" Content="0">
<meta Http-Equiv="Pragma-directive: no-cache">
<meta Http-Equiv="Cache-directive: no-cache">

Answer 2

Let's add another solution one to the bunch.

Adding a unique string at the end is a perfect solution.

example.jpg?646413154

Following solution extends this method and provides both the caching capability and fetch a new version when the image is updated.

When the image is updated, the filemtime will be changed.

<?php
$filename = "path/to/images/example.jpg";
$filemtime = filemtime($filename);
?>

Now output the image:

<img src="images/example.jpg?<?php echo $filemtime; ?>" >

Answer 3

Changing the image source is the solution. You can indeed do this by adding a timestamp or random number to the image.

Better would be to add a checksum of eg the data the image represents. This enables caching when possible.

Answer 4

i had this problem and overcoming like this.

var newtags='<div class="addedimage"><h5>preview image</h5><img src="'+one+'?nocache='+Math.floor(Math.random() * 1000)+'"></div>';

Answer 5

I checked all the answers and the best one seemed to be (which isn't):

<img src="image.png?cache=none">

at first.

However, if you add cache=none parameter (which is static "none" word), it doesn't effect anything, browser still loads from cache.

Solution to this problem was:

<img src="image.png?nocache=<?php echo time(); ?>">

where you basically add unix timestamp to make the parameter dynamic and no cache, it worked.

However, my problem was a little different: I was loading on the fly generated php chart image, and controlling the page with $_GET parameters. I wanted the image to be read from cache when the URL GET parameter stays the same, and do not cache when the GET parameters change.

To solve this problem, I needed to hash $_GET but since it is array here is the solution:

$chart_hash = md5(implode('-', $_GET));
echo "<img src='/images/mychart.png?hash=$chart_hash'>";

Edit:

Although the above solution works just fine, sometimes you want to serve the cached version UNTIL the file is changed. (with the above solution, it disables the cache for that image completely) So, to serve cached image from browser UNTIL there is a change in the image file use:

echo "<img src='/images/mychart.png?hash=" . filemtime('mychart.png') . "'>";

filemtime() gets file modification time.

Answer 6

Simple, send one header location.

My site, contains one image, and after upload the image, there not change, then I add this code:

<?php header("Location: pagelocalimage.php"); ?>

Work's for me.