Php 缓存动态生成的图像

我正在使用PHP脚本生成一些图像。
我想缓存图像，这样浏览器就不必每次都加载它们。 我添加了以下标题：

'max-age' => 3600
'Etag' => md5($image->getSlug())
'last-modified' => $image->getUpdatedAt()
'Vary' => 'Accept-Encoding'
'content-length' => (size of the image)
'Content-type' => 'image/jpeg'

但图像不会被缓存，并且每次都由浏览器加载

响应头如下所示（使用Firebug）：

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有人知道这里出了什么问题吗？

您需要计算并添加一个Expires:header。例如：

Expires: Fri, 30 Oct 2011 14:19:41 GMT

<?php
error_reporting(0); //disable error reporting as it will corrupt the image
session_start(); //start a php session
$date = date(DATE_RFC822);
//some code to connect to a mysql database
$query = mysqli_query($link, "SELECT * FROM images WHERE sessionid='$sessionid'");
if ($query and mysqli_num_rows($query) == 1) { //if mysql returned one row
    $row = mysqli_fetch_array($query); //get the row as an array
    $date = $row["date"]; //set the date to the one in the database
} else { //if the user has never seen the image before
    mysqli_query($link, "INSERT INTO images SET sessionid='$sessionid', date='$date'"); //put the session id and date into the database for later use
}
header("Last-Modified: $date");
//some code that would generate and send the image

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强制缓存图像的一种方法是将

Last Modified

标记设置为创建要使用的图像的日期和时间。例如：

Expires: Fri, 30 Oct 2011 14:19:41 GMT

<?php
error_reporting(0); //disable error reporting as it will corrupt the image
session_start(); //start a php session
$date = date(DATE_RFC822);
//some code to connect to a mysql database
$query = mysqli_query($link, "SELECT * FROM images WHERE sessionid='$sessionid'");
if ($query and mysqli_num_rows($query) == 1) { //if mysql returned one row
    $row = mysqli_fetch_array($query); //get the row as an array
    $date = $row["date"]; //set the date to the one in the database
} else { //if the user has never seen the image before
    mysqli_query($link, "INSERT INTO images SET sessionid='$sessionid', date='$date'"); //put the session id and date into the database for later use
}
header("Last-Modified: $date");
//some code that would generate and send the image

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如果你看我原来的帖子，你会发现我已经包括了上次修改的内容。@Ako啊，是的，对不起，我的不好。嗯，我想不出还有什么可以做的，除了可能使用“file\u put\u contents”保存图像的内容，然后在显示图像的页面上使用图像文件名。你知道吗？我也有同样的问题。。