Bluring Image

Hello,

I'm searching for a filter like used by google streetview to blure images of
different size/resolution. I have images uploaded by user and I wan't them
to be displayed blured in so cases. The viewing user should see that there
is an image but should not be able to view details. Bluring an image is no
problem but you haveto find out the best paramaters manualy. I need to put
this into a script (e.g. PHP) to bluring any size/resolution auf an image.

Regards,
Andreas