Image is caching, how do i stop it

using gd, php, but browser is loading cache, not image

[scratch]

I am using gd to generate images dynamically on a page, with the user able to make changes to said image. Everything works fine, but i have to right-click/reload to see the changes. It always pulls the older version although it is working perfectly.

I am assuming that i have no control over users browsers and how often they check to see if a new page. I want this to be the only thing that caches.

A. Is there a way around using a new filename each time i generate the image.

Meta stuff does not seem to work like the following
<META HTTP-EQUIV="Expires" CONTENT="Tue, 01 Jan 1980 1:00:00 GMT">
<META HTTP-EQUIV="Pragma" CONTENT="no-cache">
also the javascript load image (var image = "filename.jpg" or whatever) does not do the trick either.

B. If i have to create new images each page load for the thousands of users, how should i generate unique names for them...and how should i clean up later. An overlap would be dangerous.

I would like to keep the last version if possible so they can copy the url and be able to see it later, and i also can't let myself be overrun with temp images...thats why i would prefer to create just one image...

[crypto]

Try this:

<meta http-equiv="refresh" content="8">

This will refresh the browser every 8 seconds.

For generating unique filenames try appending the time
stamp to the filenames.

[andreasfriedrich]

Send the appropriate header [php.net] along with the image to prevent browsers from caching the image.

Andreas

[scratch]

<meta http-equiv="refresh" content="8">

Is really cool, but it makes it hard to see the page as the whole page reloads every so many seconds...

How do i add a time stamp to the image, that is the only thing i want to force a reload on.

I am generating a file from within the page that is external and then loading it into an image, so i am not sure i can affect the header without reworking the whole thing.

Is it possible to pass vars to php from html without submitting a page using javascript and then redrawing the image.

[scratch]

$filetocreate = date("U").".jpg"; it is

I give up and must give take crypto's advice for the time stamp. I'll probably code into the form a way to delete previous file as the next one is generated.

I'm really surprised that there does not seem a way to reload a picture for the user.

[crypto]

for unique filename try this:

$filetocreate=rand().date("dmYHis").".jpg";

I think this should be unique. If you want to reload the page on some specific event then try a javascript function for that event using window.location.reload() method or you can set a timer to reload the page periodically.

[Brett_Tabke]

That is really the hard way to go about it scratch.

Put your graphic or where ever the graphic is being pulled from, in a single directory. Then set the headers in that directory via an .htaccess file:

Header add Cache-Control "max-age=0"
Header add Pragma "no-cache"

That will cause everything in that directory to reload on each browser view.

That is if you are using apache. If not, switch ;-)

[scratch]

Thank you so, and i am moving to apache right now (from iis and asp) so i will be able to implement the htaccess. I've already got 87 images from debugging alone, this is a much better solution.

[Ron_Carnell]

You shouldn't have to change the file name. You just have to change the browser's perception of the file name. Add a question mark to the end of the file name, followed by a string of random numbers (current time will do fine). It will look like filename.jpg?012345. The server will ignore the passed parameter, but the browser will consider each instance as a unique file name. This is a very old trick to force pages to bypass the cache, but should work equally well with images.