How to force image (cache) update in README.rst on GitHub

Question

In one of my project I'm using an external image link to display a screenshot via the GitHub page, which automatically parses the README.rst

GitHub page of ROyWeb

I updated this screenshot on my web server several times in the last weeks and I just realised that it is not updated on the GitHub page since... well I think it never updated ;-) GitHub somehow downloaded the image and loads it from it's cache servers.

Within the README.rst, there is clearly the correct link:

Actual link to the ROyWeb screenshot

Which you can confirm, when you load the raw file:

raw README.txt on GitHub

But when I check the URL of the displayed image on the GitHub page, I get:

GitHub cached screenshot of ROyWeb

Does anyone know how to force a "recache"?

I would also be interested to know the answer to this. – b85411 Jan 09 '15 at 06:41 — b85411, Jan 09 '15 at 06:41
Then vote up the question @b85411 ; ) – tamasgal Jan 09 '15 at 08:51 — tamasgal, Jan 09 '15 at 08:51

score 85 · Accepted Answer · edited May 03 '16 at 11:22

85

curl -X PURGE {url of cached badge image}

edited May 03 '16 at 11:22

Sнаđошƒаӽ

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answered May 03 '16 at 09:41

Alex Skrypnyk

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This doesn't work for me. Is there another approach? My readme is a mess of missing images (mostly shields.io badges). Is this a known bug with any prospect of a fix? – orome Jan 19 '17 at 15:25
Doesn't do a thing for me either. – TheChymera Jul 05 '17 at 23:15
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Thats amazing! Out of curiosity, where did you find this information. I dont think PURGE is a standard http method? – Michael Aquilina May 11 '18 at 09:08
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@MichaelAquilina I don't know how he finds it but Github mentions it [here](https://help.github.com/articles/about-anonymized-image-urls/#removing-an-image-from-camos-cache). – 张实唯 Aug 27 '18 at 05:17
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This does work indeed! If it doesn't for you, press the Ctrl key while clicking refresh, you're probably getting the image from your own cache (I had to do this). – BenMorel Apr 25 '19 at 09:43
@MichaelAquilina it's mentioned in the middle of this long (5 year!) issue: https://github.com/atom/markdown-preview/issues/207 – Mike Honey Jun 13 '20 at 12:29
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Make sure to refresh with Ctrl-Shift-R to clear your browser cache. – makeworld Oct 24 '20 at 16:23
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Today this method stopped working for me (after many months of almost daily use) - its returning "Access to this site has been restricted.". I tried adding an API token - same result. The image did eventually refresh, so perhaps this is no longer necessary? – Mike Honey Nov 11 '20 at 05:21
For those who find this not working, note that the `PURGE` _is_ case-sensitive. – wbharding Jan 19 '22 at 16:04
@MikeHoney, are you still getting the restricted response, or are you still using this process? I want to do this for hundreds/thousands of images and assume I will be blocked with some type of rate limiting. It is working for me on single requests, though. – Tim Ramsey Aug 16 '23 at 20:36
@TimRamsey tbh I gave up on github as a platform for dynamic images – Mike Honey Aug 20 '23 at 09:31

Sibeesh Venu · Answer 2 · 2021-04-15T09:22:56.100

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There is also a trick that can be useful. It is nothing but just adding a question mark at the end of the image extension.

![This is an automated blog post image using Azure Function](https://customurl.blob.core.windows.net/github/latestpost.png?)

See the question mark (?) at the end. You can also see the live example here in my GitHub profile.

You can see more about this here.

edited Apr 15 '21 at 09:22

answered Feb 03 '21 at 15:20

Sibeesh Venu

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You are amazing! – unobatbayar Apr 15 '21 at 09:21
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Based @Sibeesh Venu – NoahVerner Feb 26 '22 at 14:21
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This should be the best answer! – Míng Aug 25 '22 at 03:16
This seems to work for the first request, but if you update the image it does not update on subsequent requests for me. – Tim Ramsey Aug 16 '23 at 20:32

score 7 · Answer 3 · answered Mar 31 '17 at 09:44

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I had a look at what shields.io does.

It sets this header (Source):

Cache-Control: max-age=2592000

answered Mar 31 '17 at 09:44

User

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I had seen that idea [here](https://github.com/github/markup/issues/224) but had no idea what syntax to use with a raw URL. Following your second link showed me how to do it. Thanks. – Mars Aug 01 '17 at 04:13

score 2 · Answer 4 · answered Jan 12 '15 at 00:59

I believe I've understood how to do this now. Instead of serving a raw png file for example, serve the image through a php file (many examples on SO).

Once you're displaying the image with PHP, add the following headers:

header('Cache-Control: no-cache');
header('Expires: ' . gmdate('D, d M Y H:i:s \G\M\T', time() - 36000));

By setting the no-cache and having the cache expire in the past, I have found that GitHub's CDN updates the images automatically on every refresh.

How to force image (cache) update in README.rst on GitHub

4 Answers4