Serve image with PHP script vs direct loading an image

Question

I want to monitor how often some external images are loaded. So my idea is instead of giving a uri directly like this:

www.site.com/image1.jpg

I can create a PHP script which reads the image, so I built a PHP file and my HTML would look like this:

<img src="www.site.com/serveImage.php?img=image1.jpg">

but I don't know how to read the image from disk and return it. Would I return a byte array or set the content type?

Kind regards, Michel

Answer 1

Sending images through a script is nice for other things like resizing and caching on demand.

As answered by Pascal MARTIN the function readfile and these headers are the requirements:

• Content-Type
  • The mime type of this content
  • Example: header('Content-Type: image/gif');
  • See the function mime_content_type
  • Types
    • image/gif
    • image/jpeg
    • image/png

But beside the obvious content-type you should also look at other headers such as:

• Content-Length
  • The length of the response body in octets (8-bit bytes)
  • Example: header('Content-Length: 348');
  • See the function filesize
  • Allows the connectio to be better used.
• Last-Modified
  • The last modified date for the requested object, in RFC 2822 format
  • Example: header('Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT');
  • See the function filemtime and date to format it into the required RFC 2822 format
    • Example: header('Last-Modified: '.date(DATE_RFC2822, filemtime($filename)));
  • You can exit the script after sending a 304 if the file modified time is the same.
• status code
  • Example: header("HTTP/1.1 304 Not Modified");
  • you can exit now and not send the image one more time

For last modified time, look for this in $_SERVER

• If-Modified-Since
  • Allows a 304 Not Modified to be returned if content is unchanged
  • Example: If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
  • Is in $_SERVER with the key http_if_modified_since

List of HTTP header responses

Answer 2

To achieve something like this, your script will need to :

• send the right headers, which depend on the type of the image : image/gif, image/png, image/jpeg, ...
• send the data of the image
• making sure nothing else is sent (no white space, no nothing)

This is done with the header function, with some code like this :

header("Content-type: image/gif");

Or

header("Content-type: image/jpeg");

or whatever, depending on the type of the image.

To send the data of the image, you can use the readfile function :

Reads a file and writes it to the output buffer.

This way, in one function, you both read the file, and output its content.

As a sidenote :

• you must put some security in place, to ensure users can't request anything they want via your script : you must make sure it only serves images, from the directory you expect ; nothing like serveImage.php?file=/etc/passwd should be OK, for instance.
• If you're just willing to get the number of times a file was loaded each day, parsing Apache's log file might be a good idea (via a batch run by cron each day at 00:05, that parses the log of the day before, for instance) ; you won't have real-time statistics, but it will require less resources on your server (no PHP to serve static files)

Answer 3

I use the "passthru" function to call "cat" command, like this:

header('Content-type: image/jpeg');
passthru('cat /path/to/image/file.jpg');

Works on Linux. Saves resources.