blocks|key|1586921|text|对于这个问题，一种常见而简单的解决方案是为每个动态图像请求添加一个随机生成的查询字符串。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1586922|所以，举例来说-|1586923|<img+src="image.png"+/>|code-block|syntax|javascript|1586924|会变成|1586925|<img+src="image.png?dummy=8484744"+/>|1586926|或|1586927|<img+src="image.png?dummy=371662"+/>|1586928|从web服务器的角度来看，访问相同的文件，但是从浏览器的角度来看，不能执行高速缓存。|1586929|随机数的生成既可以发生在提供页面时的服务器上(只要确保页面本身没有被缓存...)，也可以发生在客户端(使用JavaScript)。|1586930|您将需要验证您的web服务器是否可以处理此技巧。|1586931|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|10|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|12|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|13|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|14|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|15|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|16|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|17|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

A common and simple solution to this problem that feels like a hack but is fairly portable is to add a randomly generated query string to each request for the dynamic image.

So, for example -

<pre><code>&lt;img src="image.png" /&gt;
</code></pre>

Would become

<pre><code>&lt;img src="image.png?dummy=8484744" /&gt;
</code></pre>

Or

<pre><code>&lt;img src="image.png?dummy=371662" /&gt;
</code></pre>

From the point of view of the web-server the same file is accessed, but from the point of view of the browser no caching can be performed.

The random number generation can happen either on the server when serving the page (just make sure the page itself isn't cached...), or on the client (using JavaScript).

You will need to verify whether your web-server can cope with this trick.

blocks|key|1586850|text|浏览器缓存策略可以通过HTTP标头进行控制。记住，它们只是一个提示，真的。由于浏览器在这个(和任何其他)字段中非常不一致，您将需要几个头文件才能在一系列浏览器上获得所需的效果。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1586851|header+("Pragma-directive:+no-cache");
header+("Cache-directive:+no-cache");
header+("Cache-control:+no-cache");
header+("Pragma:+no-cache");
header+("Expires:+0");|code-block|syntax|javascript|1586852|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Browser caching strategies can be controlled by HTTP headers. Remember that they are just a hint, really. Since browsers are terribly inconsistent in this (and any other) field, you'll need several headers to get the desired effect on a range of browsers.

<pre><code>header ("Pragma-directive: no-cache");
header ("Cache-directive: no-cache");
header ("Cache-control: no-cache");
header ("Pragma: no-cache");
header ("Expires: 0");
</code></pre>

blocks|key|1586970|text|如果您需要使用javascript在浏览器中动态执行此操作，这里有一个示例...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1586971|<img+id=graph+alt=""+
++src="http://www.kitco.com/images/live/gold.gif"+
++/>

<script+language="javascript"+type="text/javascript">
++++var+d+=+new+Date();+
++++document.getElementById("graph").src+=+
++++++"http://www.kitco.com/images/live/gold.gif?ver="+%2B+
+++++++d.getTime();
</script>|code-block|syntax|javascript|1586972|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

If you need to do it dynamically in the browser using javascript, here is an example...

<pre><code>&lt;img id=graph alt="" 
 src="http://www.kitco.com/images/live/gold.gif" 
 /&gt;

&lt;script language="javascript" type="text/javascript"&gt;
 var d = new Date(); 
 document.getElementById("graph").src = 
 "http://www.kitco.com/images/live/gold.gif?ver=" + 
 d.getTime();
&lt;/script&gt;
</code></pre>

blocks|key|1372156|text|我只是在寻找一个解决方案，上面的答案在我的情况下不起作用(我没有足够的声誉来评论它们)。事实证明，至少对于我的用例和我使用的浏览器(OSX上的Chrome)来说，唯一阻止缓存的似乎是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1372157|Cache-Control+=+'no-store'|code-block|syntax|javascript|1372158|为了完整性，我现在使用所有3个‘无缓存，无存储，必须重新验证’|1372159|因此在我的例子中(用Python在Flask中提供动态生成的图像)，我必须做以下工作，希望能在尽可能多的浏览器中工作……|1372160|def+make_uncached_response(inFile):
++++response+=+make_response(inFile)
++++response.headers['Pragma-Directive']+=+'no-cache'
++++response.headers['Cache-Directive']+=+'no-cache'
++++response.headers['Cache-Control']+=+'no-cache,+no-store,+must-revalidate'
++++response.headers['Pragma']+=+'no-cache'
++++response.headers['Expires']+=+'0'
++++return+response|1372161|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I was just looking for a solution to this, and the answers above didn't work in my case (and I have insufficient reputation to comment on them). It turns out that, at least for my use-case and the browser I was using (Chrome on OSX), the only thing that seemed to prevent caching was:

<pre><code>Cache-Control = 'no-store'
</code></pre>

For completeness i'm now using all 3 of 'no-cache, no-store, must-revalidate'

So in my case (serving dynamically generated images out of Flask in Python), I had to do the following to hopefully work in as many browsers as possible...

<pre><code>def make_uncached_response(inFile):
 response = make_response(inFile)
 response.headers['Pragma-Directive'] = 'no-cache'
 response.headers['Cache-Directive'] = 'no-cache'
 response.headers['Cache-Control'] = 'no-cache, no-store, must-revalidate'
 response.headers['Pragma'] = 'no-cache'
 response.headers['Expires'] = '0'
 return response
</code></pre>

blocks|key|1371942|text|我知道这是一个古老的话题，但它在谷歌中排名很高。我发现把这个放到你的头中效果很好；|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1371943|<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">|code-block|syntax|javascript|1371944|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

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

<pre><code>&lt;meta Http-Equiv="Cache-Control" Content="no-cache"&gt;
&lt;meta Http-Equiv="Pragma" Content="no-cache"&gt;
&lt;meta Http-Equiv="Expires" Content="0"&gt;
&lt;meta Http-Equiv="Pragma-directive: no-cache"&gt;
&lt;meta Http-Equiv="Cache-directive: no-cache"&gt;
</code></pre>

blocks|key|1587051|text|更改图像源是解决方案。您确实可以通过向图像添加时间戳或随机数来做到这一点。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1587052|更好的方法是添加一个校验和，例如图像表示的数据。这将在可能的情况下启用缓存。|1587053|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

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.

blocks|key|1587259|text|我有这个问题，就像这样克服。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1587260|var+newtags='<div+class="addedimage"><h5>preview+image</h5><img+src="'%2Bone%2B'?nocache='%2BMath.floor(Math.random()+*+1000)%2B'"></div>';|code-block|syntax|javascript|1587261|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

i had this problem and overcoming like this. 

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

blocks|key|1587100|text|如果你有一个硬编码的图像URL，例如：http://example.com/image.jpg，你可以使用php为你的图像添加标题。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1587101|首先，您必须让apache将您的jpg处理为php。查看此处：Is+it+possible+to+execute+PHP+with+extension+file.php.jpg?|1587102|从文件中加载图像(imagecreatefromjpeg)，然后添加前面答案中的标题。使用php函数header添加头部。|1587103|然后使用imagejpeg函数输出图像。|1587104|请注意，让php处理jpg图像是非常不安全的。另外请注意，我还没有测试过这个解决方案，所以让它工作是你的事。|1587105|entityMap|0|LINK|mutability|MUTABLE|url|http://example.com/image.jpg|1|https://stackoverflow.com/questions/8025236/is-it-possible-to-execute-php-with-extension-file-php-jpg^0|J|S|0|0|V|1M|1|0|0|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@$A|W|B|X|1|Y]]|C|$]]|$1|D|3|E|5|6|7|Z|8|@]|9|@$A|10|B|11|1|12]]|C|$]]|$1|F|3|G|5|6|7|13|8|@]|9|@]|C|$]]|$1|H|3|I|5|6|7|14|8|@]|9|@]|C|$]]|$1|J|3|K|5|6|7|15|8|@]|9|@]|C|$]]|$1|L|3|-4|5|6|7|16|8|@]|9|@]|C|$]]]|M|$N|$5|O|P|Q|C|$R|S]]|T|$5|O|P|Q|C|$R|U]]]]

If you have a hardcoded image URL, for example: <a href="http://example.com/image.jpg" rel="nofollow noreferrer">http://example.com/image.jpg</a> you can use php to add headers to your image.

First you will have to make apache process your jpg as php. 
See here:
<a href="https://stackoverflow.com/questions/8025236/is-it-possible-to-execute-php-with-extension-file-php-jpg">Is it possible to execute PHP with extension file.php.jpg?</a>

Load the image (imagecreatefromjpeg) from file then add the headers from previous answers. Use php function header to add the headers. 

Then output the image with the imagejpeg function.

Please notice that it's very insecure to let php process jpg images. Also please be aware I haven't tested this solution so it is up to you to make it work.

blocks|key|1372101|text|很简单，发送一个头位置。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1372102|我的网站，包含一张图片，上传图片后，没有变化，然后我添加了以下代码：|1372103|<?php+header("Location:+pagelocalimage.php");+?>|code-block|syntax|javascript|1372104|这是我的工作。|1372105|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Simple, send one header location.

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

<pre><code>&lt;?php header("Location: pagelocalimage.php"); ?&gt;
</code></pre>

Work's for me.

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 dynamically by me?

Note: I have to use same name for the created images over time.

Disable cache for some images

服务器

Python

我使用PHP库生成一些图像。有时浏览器不加载新生成的文件。如何才能仅为我动态创建的图像禁用缓存？注意:随着时间的推移，我必须为创建的图像使用相同的名称。

问禁用某些图像的缓存
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回答 9

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