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Asked: 2026-06-08T06:51:05+00:00

Probably a bit of general question, even tho’ it’s specific to a certain type

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Probably a bit of general question, even tho’ it’s specific to a certain type of website/application, but will give it a shot regardless. I’m a bit confused wether or not I should be caching my thumbnails for my current project, normally I would, but I’m not sure about this project. I’ll explain my situation better to give a better understanding.

I have a stock photo website, for celebrity, news and sport photos, that show authorised clients (newspapers & magazines) our entire library. These photos have some value and I have gone to great measures to ensure the larger photos are either hidden on Amazon S3, or above the root directory, with expiring and hashed links, so I don’t want to jeopardize my photos by adding a cache when I shouldn’t be or adding an incorrect cache. A typical user may search for a photo and never see it again or they might save a photo to their favorites and see it twice-daily. A user could also browse 10,000 photos in a couple of minutes.

My question is; should I have no cache at all or have a limited cache, for say, 1 hour, or 1 day? If I set a cache expiry for a photo, will that be accessible to my client on their browser, under say ‘cached images’? Is there any other security issues with caching valuable photos?

I know about screen-grabbing, printing and the rule; if you don’t want it stolen, don’t put it on the web, but I want to do the best I can in my application for security and speed.

I’m using PHP (5.2.17) for loading images from Amazon to my client’s browser using PHP’s ReadFile() and IMG elements like <img src="loadImage.php?p=2342dfsfsdfwf2dfsf">.

To clarify what type of caching:

<?php
header("Expires: Sat, 26 Jul 1997 05:00:00 GMT");
header("Content-Type: image/jpeg");
readfile($url);
?>
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1 Answer

  1. Editorial Team

    If you are extremely concerned about the security of the images, then I would say do not cache them at the expense of using more bandwidth (and a slower loading time). If you are more concerned about bandwidth usage than security, cache them.

    However, if they are truly thumbnails, they should have little value to a user if they are small, of low quality, etc. One solution would be to watermark the images.

    In theory, it is possible to extract images from a browser’s cache (http://protechgeek.com/how-to-extract-images-from-browser-cache/), so if they are cached, they can be retrieved. Even easier, someone can screen grab as you mentioned, or right-click and copy/paste. A watermark is the only solution to this.

    tl;dr

    In my opinion, I would not think it’s worth the extra bandwidth hit and increased loading time for a minimal security increase. Use watermarks instead. There’s a reason that the majority of stock photo websites use watermarks– they are the only way to prevent someone from outright stealing the image (even though, depending on the image and watermark, it can be removed convincingly by a skilled Photoshop user)

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