I have used Umbraco and there is very nice ImageGen library there which allows to resize images 'on the fly' and cashes processed images.
Is there something similar to it I can use outside Umbraco?
(I thought I could use ImageGen without Umbraco but it looks like it is not free)
Thanks
I realise this question is quite old, but since I still stumbled across it, I thought I should post my findings.
http://imageprocessor.org/ seems to be a relatively new library that is free and open source, and has quite a number of features too!