Does someone know a good web service to resize images ? Either an open source (PHP/Python/Ruby) application, or a company providing a web service api.

• php
• python
• ruby
• web-services
• image-processing

So you're asking for a website?

http://www.picnik.com/ is what Flickr uses.

http://www.shrinkpictures.com/

Make your own service at Utility Mill (http://utilitymill.com). Here's one that I wrote that adds a simulated gallery wrap - http://utilitymill.com/utility/Gallery_Wrap_Image. Define your own interface, parameters, processing logic, and you get not only an interactive web service, but you also get a callable API.

Another alternative is the image processing web service at www.lightspun.com .

PHP provides image resizing support using image magick. Smart Image Resizer is a PHP script ready for use. Look at http://shiftingpixel.com/2008/03/03/smart-image-resizer/

To build your own PHP app, look at http://www.php.net/manual/de/ref.image.php