Best way to deal with image thumbnails on news web site (custom CMS based on codeigniter)?
Your best bet is to create images on the fly + use CDN like Amazon Cloudfront to cache the resized versions of your source image.
I’ve been using CodeIgniter for a number of years to build websites where lots of different sizes of images are used throughout the website. At the beginning I used to create every size needed out of the original image during the upload process (could easily end up with more than 5 thumbnails). This proved to be delivering the best performance – whenever you need an image of the certain size you just include it with no additional PHP processing. However I noticed that I end up with a huge number of images on the server, where the older ones may not even be used that often (e.g.: articles older than a year). Plus developing this way takes longer.
Then I started creating images on the fly, firstly using 3rd party libraries and later developed my own interface for CodeIgniter. This saves a lot of time, because during the upload process you save an original version of the image not worrying about resized versions. When displaying an image in the front end, all you normally need to do is to pass certain dimensions of the image required. Doing this way, not only you can get 5-6 versions of the image, but as many as you need. Also that’s a solution for the future when you redesign your website where the different sized images might be needed! What would you do when none of your 5 thumbnail options are no longer valid and you need different sizes?
You’re right, resizing an image on the fly can really be CPU consuming operation (especially when the large images are involved), therefore caching is a must. You can cache images right on your server or get CDN on top of that.To keep the server tidy I normally run a cron job to delete on-the-fly images older than let's say a week. That saves space + doesn't cause harm - whenever image is needed to display, it'll just get recreated.
Check out timthumb, it's a script that resizes images on the fly and stores them in a cache. It's a simple as including an image tag with parameters in the URL.
ALso check this link which looks promising http://www.jenssegers.be/blog/31/Codeigniter-resizing-and-cropping-images-on-the-fly-continued
I love the way Drupal manage this. In Drupal 6 there was a module called imagecache (now is in core in Drupal 7, but functionality is very similar), which basically stores presets for images (image sizes, transformations, effects...) and when the visitor ask for an image the module generate different images based on presets and serve this images. This way you upload an image but have different images for different purposes.
The module has a really useful feature, if you want to change one preset, you can "flush" all the images related with that preset, so the visitors can see the changes.
Of course there are many other modules in Drupal related to imagecache or image styles, that add other effects like watermarks...
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